<p>Salicylic acid (SA) is a central plant defense signal. It is not only required for closing the stomata upon infection to prevent pathogens from entering into the plant apoplast, but also mediates defense responses activated by pathogen-originated microbe-associated molecular patterns (MAMPs) and effectors in the infected tissues. In addition, SA is a necessary and sufficient signal for systemic acquired resistance (SAR). In <italic>Arabidopsis</italic> <italic>thaliana</italic>, SA level increases in response to pathogen attack, which is essential for activating defense responses. This SA accumulation involves transcriptional activation of several genes including <italic>ICS1</italic> (<italic>ISOCHORISMATE</italic> <italic>SYNTHASE</italic> <italic>1</italic>), <italic>EDS5</italic> (<italic>ENHANCED</italic> <italic>DISEASE</italic> <italic>SUSCEPTIBILITY</italic> <italic>5</italic>), <italic>EDS1</italic> (<italic>ENHANCED</italic> <italic>DISEASE</italic> <italic>SUSCEPTIBILITY</italic> <italic>1</italic>), <italic>PAD4</italic> (<italic>PHYTOALEXIN-DEFICIENT</italic> <italic>4</italic>) and <italic>PBS3</italic> (<italic>avrPphB</italic> <italic>SUSCEPTIBLE</italic> <italic>3</italic>). However, it is not well understood how pathogenic signals induce these SA accumulation genes. Interestingly, our time-course transcriptome analysis showed that these five genes share a similar pathogen-induced expression pattern, suggesting the existence of common transcription factors (TFs). Through yeast-one-hybrid screening, a TF NTL9 was identified for its interactions with the promoters of the SA accumulation genes. Preferentially expressed in guard cells, NTL9 activates the expression of SA accumulation genes in guard cells. The <italic>ntl9</italic> mutant is defective in pathogen-induced stomatal closure mediated by a well-characterized MAMP, flg22. Consistent with the stomatal closure defect, the <italic>ntl9</italic> mutant exhibits elevated susceptibility to surface-inoculated pathogens. The stomatal closure defect of the <italic>ntl9</italic> mutant can be rescued by exogenous application of SA, demonstrating that NTL9 acts upstream of SA in stomatal closure response. These results suggest that NTL9-mediated activation of SA accumulation genes is essential for MAMP-triggered stomatal closure.</p><p>While plants induce SA to activate defense responses, pathogens can also produce virulence factors to counteract the effects of SA. Coronatine is one such virulence factor produced by <italic>Pseudomonas</italic> <italic>syringae</italic>. Coronatine is known to promote opening of stomata for bacterial entry, bacterial growth in the apoplast, systemic susceptibility and development of disease symptoms such as chlorosis. In the process of examining the mechanisms underlying coronatine-mediated virulence, three homologous TFs, ANAC019, ANAC055 and ANAC072, were found to be activated by coronatine directly through the TF, MYC2. Genetic characterization of these three TF mutants revealed that these TFs mediate multiple virulence effects of coronatine by inhibiting SA accumulation. To exert this inhibitory effect, these TFs repress <italic>ICS1</italic> and activate <italic>BSMT1</italic>, genes involved in SA biosynthesis and inactivation modification, respectively. Thus, a signaling cascade downstream of coronatine was illustrated to dampen SA-mediated defense responses through differential transcriptional regulation of genes related to SA level.</p><p>Taken together, my dissertation studies revealed novel transcriptional regulation of SA production and demonstrated that this transcriptional regulation is a vital point not only for plant defense activation but also for pathogen manipulation to counteract defense responses. Further studies on the interplay of this transcriptional regulation by different TFs would broaden our understanding about the dynamics of plant-pathogen interaction.</p> / Dissertation

Thesis (PhD)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: Bacterial canker of stone fruit, caused by Pseudomonas syringae pv. syringae, is one of the most destructive crop diseases in South Africa. Chemical control has failed completely and effective long-term management strategies will have to rely on the breeding of resistant host trees. To assist in such breeding programmes, investigations into the molecular basis of the interaction between P. s. pv. syringae and stone fruit trees have been undertaken in collaboration with the ARC-Fruit, Wine and Vine Research Institute in Stellenbosch. The aim of this dissertation was to clone and identify genes that are involved in interaction between the bacterial canker pathogen and stone fruit trees. In the first part of the study, the harpin encoding gene of a local strain of the pathogen, P. s. pv. syringae NV, was amplified in a polymerase chain reaction (PCR) strategy with primers based on the hrpAZB sequences of the bean pathogen, P. s. pv. syringae 61. Sequencing of this hrpZpssNvgene revealed a high degree of homology (96%) between the harpin encoding genes and harpin proteins of the two strains. The hrpZpssNvgene was subsequently cloned into the pMAL-c2 expression vector and expressed in Escherichia co/i. This system was used for the production of purified, biologically active, recombinant HrpZpSSNV protein. In the second part of the study, differential display (DD) technology was used to identify genes that are induced in stone fruit trees in response to P. s. pv. syringae and/or its harpin elicitor. For this purpose, actively growing shoots of two Prunus sa/icina cultivars, the moderately resistant cv. 'Laetitia' and the highly susceptible cv. 'Songold' were treated with recombinant harpinpssNvprotein or live P. s. pv. syringae NV bacteria. An untreated control and wounding control was included in the experiment. Total RNA was isolated for comparative mRNA analysis 24 hours after treatment. DD profiles were generated with fifteen primer combinations. Eight candidate bands were re-amplified, cloned and sequenced. Reverse transcription PCR was employed to verify the expression patterns of the cloned bands in the original RNA sample set. Two bands, DDc and DD4 were shown to be differentially expressed between treatments and/or cultivars, while no differences in the expression levels of the remaining six bands (DDa, DDe, DD3, DD5, DD6 and DD7) were observed. BLAST similarity searches yielded significant matches for DDe, DD4 and DD7 with plant defense-related genes. / AFRIKAANSE OPSOMMING: Bakteriese kanker van steenvrugte, wat deur Pseudomonas syringae pv. syringae veroorsaak word, is een van die mees verwoestende siektes van landbougewasse in Suid-Afrika. Chemiese beheermaatreëls het geheel en al misluk en effektiewe langtermyn beheerstrategieë sal op die teling van weerstandbiedende gasheerbome moet staatmaak. Ondersoeke na die molekulêre basis van die interaksie tussen P. s. pv. syringae en steenvrugbome is in samewerking met die LNR-Vrugte-, Wyn- en Wingerdnavorsingsinstituut in Stellenbosch van stapel gestuur om tot sulke telingsprogramme by te dra. Die doelwit van hierdie proefskrif was om gene wat betrokke is in die interaksie tussen die bakteriese kanker patogeen en steenvrugbome te kloneer en te identifiseer. In die eerste gedeelte van die studie is die harpien-koderende geen van 'n plaaslike ras van die patogeen, P. s. pv. syringae NV, geamplifiseer in 'n polimerase kettingreaksie (PKR)-strategie met peilers wat op die hrpAZB-geenopeenvolgings van die boontjiepatogeen, P. s. pv. syringae 61, gebaseer is. Volgordebepaling van hierdie hrpZpssNv-geen het 'n hoë vlak van homologie (96%) tussen die harpien-koderende gene en harpien proteïene van die twee rasse getoon. Die hrpZpssNv-geen is vervolgens in die uitdrukkingsvektor pMAL-c2 gekloneer en uitgedruk in Escherichia coli. Hierdie sisteem is vir die produksie van suiwer, biologies-aktiewe, rekombinante HrpZpssNv-proteingebruik. In die tweede gedeelte van die studie is die differensiaalvertoon (DD) tegniek gebruik om gene te identifiseer wat deur P. s. pv. syringae en/of sy harpien elisitar in steenvrugbome geïnduseer word. Vir hierdie doel is aktief-groeiende lote van twee Prunus sa/icina kultivars, die matig weerstandbiedende kv. 'Laetitia' en die hoogs vatbare kv. 'Songold', met rekombinante harpienpssNvproteïen of lewende P. s. pv. syringae NV bakterieë behandel. 'n Onbehandelde- en verwondingskontrole is in die eksperiment ingesluit. Totale RNA is 24 uur na behandeling vir vergelykende mRNA-analise geïsoleer. DD-profiele is met vyftien peilerkombinasies gegenereer. Agt kandidaatbande is geheramplifiseer en gekloneer, waarna hul DNA-opeenvolgings bepaal is. Trutranskriptase-PKR is gebruik om die ekspressiepatrone van die gekloneerde bande in die oorspronklike RNA monsters na te gaan. Daar is vasgestel dat twee van die bande, DDc en DD4, differensieel tussen kultivars en/of behandelings uitgedruk is, terwyl geen verskille in die ekspressievlakke van die oorblywende ses bande (DDa, DOe, 003, DOS, 006 en DO7) waargeneem is nie. BLAST-soektogte het betekenisvolle ooreenkomste vir DDe, DD4 en DD7 met plant weerstandsgeassosieerde gene opgelewer.

An der pflanzlichen Plasmamembran geschieht die erste Wahrnehmung von mikrobiellen Molekülen, die MAMPs genannt werden. MAMP/PAMP Rezeptoren leiten frühe Abwehrantworten, wie die Produktion von reaktiven Sauerstoffspezies (ROS), externe Alkalisierung oder Ethylen, ein. Die Arabidopsis FLS2 rezeptorartige Kinase (RLK) stellt einen plasmamembran-lokalisierten MAMP Rezeptor dar, der über die Detektion des Flagellum von Pseudomonas species, eine basale Immunität in Arabidopsis thaliana vermittelt. Flg22, der kürzeste aktive Teil des bakteriellen Flagellins besteht aus 22 Aminosäuren und ist der bestuntersuchte bakterielle Elizitor. In der vorliegenden Arbeit zeigen wir eine starke Beteiligung von Ionenflüssen in der Initiationsphase der basalen Immunität. Unsere Messungen an intakten Arabidopsis Pflanzen und Pflanzengeweben sind in höchstem Masse reproduzierbar und öffnen eine neue Sicht, über die Natur von Ionentransporten in der Pflanzen - Mikroben Interaktion. Als Antwort auf die Applikation von flg22, haben wir nach einer Verzögerungsphase von etwa 2 Minuten eine transiente, dosis-abhängige Depolarisation (EC50=0,2 nM) in Mesophyll- und Wurzelhaarzellen von A. thaliana messen können. Das um 2 Aminsäuren kürzere Peptid flg22 &#916;2 oder das Flagellin anderer Bakterien (Agrobacterium or Azospirillum) führten zu keiner Membrandepolarisation. Ebenso konnten keine Membranspannungsänderungen in dem Arabidopsis Ökotypen Ws-0, dem der funktionelle FLS2 Rezeptor fehlt, detektiert werden. Die Komplementation von Ws-0 Pflanzen mit dem intakten FLS2 Rezeptorgen rief eine Resensibilisierung für flg22 hervor. Mit dem EF-Tu Elizitor Peptid aus E.coli, welches durch den Arabidopsis MAMP Rezeptor EFR detektiert wird, wurden ähnliche Ergebnisse erzielt. Auf der Basis von Aequorin wurden Kalzium-induzierte Lumineszenzmessungen durchgeführt, in denen ein transienter Anstieg der zytosolischen Kalziumkonzentration als Antwort auf die Applikation von flg22 gemessen werden konnte. Dosis-Abhängigkeitsmessungen von flg22 und [Ca2+]cyt wiesen zwei unterschiedliche EC50 Werte, von 43 ± 2 pM und 67 ± 42 nM, auf. Möglicherweise wird auf zwei verschiedene Kalziumpools zugegriffen oder es werden zwei verschiedene Kalziumleitfähigkeiten aktiviert. Die Ionenkanalaktivierung und folgende Depolarisation benötigt die aktive Rezeptorkinase. In bak1-4 Arabidopsis Pflanzen, in denen die FLS2 Untereinheit BAK1 – eine weitverbreitete RLK, die auch mit dem Brassinosteroid Rezeptor assoziiert ist – fehlt, konnte keine Depolarisation als Antwort auf flg22 gemessen werden. Arabidopsis Mesophyllzellen zeigten die typische Alkalisierung des Apoplasten als Antwort auf flg22. Nicht-invasive MIFETM Experimente mit Ionen-selektiven Elektroden ergaben, dass der pH-Anstieg durch einen Einstrom von Protonen hervorgerufen wurde. Zusätzlich wurde ein Ausstrom von Chlorid und Kalium aufgezeichnet. Ähnlich wie das Kalziumsignal waren alle detektierten Ionenströme von transienter Natur. Im zweiten Ansatz wurden Membranpotential-Messungen durchgeführt, während in der externen Lösung die Konzentrationen von Protonen, Kalzium, Kalium oder Anionen variiert wurden. Nur eine Änderung des Anionengradienten hatte einen entscheidenden Einfluss auf die flg22-induzierte Depolarisation, was die Wichtigkeit der Anionenkanalaktivierung unterstreicht. Exudat Analysen ergaben, dass Nitrat das bevorzugt transportierte Ion ist. Unter zahlreichen getesteten Ionenkanalblockern erwies sich lediglich Lanthan als effektiver Blocker des flg22-induzierten zytosolichen Kalziumanstiegs, des Protoneneinstroms und der Membrandepolarisation. Da Lanthan bekanntlich unspezifische Kationenkanäle blockt, kann man an diesem Punkt davon ausgehen, dass Kalzium-aktivierte Anionenkanäle die Membrandepolarisation vermitteln und darauf eine Aktivierung von auswärtsgerichteten Kaliumkanälen folgt. Zukünftige Studien mit Doppelläufigen-Mikroelektroden Spannungsklemmexperimenten oder externen ionenselektiven Elektroden an intakten Schliesszellen werden helfen weitere Informationen über die Natur der Ionenkanäle in der basalen Immunität oder generell in der Pflanzen-Mikroben Interaktion zu erhalten. Über die elektrophysiologische Charakterisierung der multiplen Ionenströme in der basalen Immunität hinaus, ist natürlich der nächste wichtige Schritt das oder die Gene zu finden, die für die Ionenkanäle oder Transporter kodieren, die durch nicht nekrotisierende Elizitoren wie flg22 in der basalen Immunantwort in Pflanzen aktiviert werden. / The plant plasma membrane represents the first site for recognition of microbial patterns called MAMPs. MAMP receptors mediate early defense responses including production of reactive oxygen species (ROS), external alkalinisation or ethylene. The Arabidopsis FLS2 receptor-like kinase (RLK) represents a plasma-membrane localized MAMP receptor that provides for innate immunity in Arabidopsis thaliana plants by specifically recognizing the flagellum (flg) of Pseudomonas species. Flg22, the shortest active part of flagellin, composed by 22 aminoacids is the best established bacterial elicitor that. About the role of ion channels in innate immunity nothing was known yet. In the current work we show a strong involvement of ion fluxes in the initiating phase of innate immunity. Our measurements on intact Arabidopsis plants and plant tissues are highly reproducible and open a new view of ion channel functions in plant microbe interactions. In response to the application of flg22, after a delay of about 2 minutes, we recorded a transient, dose-dependent depolarization (EC50=0.2 nM) in mesophyll and root hair cells of A. thaliana. Following wash-out of the peptide elicitor and recovery of the membrane potential to resting potential values within 70 ± 9 min, depolarizations could be elicited several times. No membrane depolarization was evoked upon application of flg22&#916;2, a truncated flg22 peptide, or by application of flagellin from other bacteria (Agrobacterium or Azospirillum). Likewise, depolarization was not observed in the natural knockout mutant of the Arabidopsis ecotype Ws-0 lacking the functional FLS2 receptor. Complementation of transgenic Ws-0 plants with the functional FLS2 receptor restored flg22 sensitivity, indicating that FLS2 is essential for flg22 evoked membrane potential changes. Similar results were obtained using the E. coli EF-Tu elicitor peptide elf18, which is recognized by the Arabidopsis MAMP receptor EFR. Aequorin based calcium measurements allowed us to record a transient increase in cytosolic calcium concentration in response to applied flg22. Dose-response studies revealed two distinct EC50 values for the calcium response of 43 ± 2 pM and 67 ± 42 nM respectively. This indicates that two different calcium pools or two different calcium permeabilities in the plasma membrane were activated by flg22. In line with a requirement of receptor-kinase activity for ion channel activation and subsequent depolarization, the latter was completely blocked by the kinase inhibitor K-252a. In bak1-4 Arabidopsis plants, lacking the FLS2 subunit BAK1 – a promiscuous RLK also associated with the brassinosteroid receptor - no depolarisation was measured in response to flg22. This indicated that both RLKs – FLS2 and BAK1 – are required for flagellin induced ion channel activation. Arabidopsis mesophyll cells showed the typical alkalinization of the apoplast in response to flg22. Noninvasive experiments with vibrating ion-selective electrodes revealed that this pH rise was due to an influx of protons. In addition an efflux of chloride and potassium was recorded. All fluxes were transient in nature, as was the observed calcium signal. Simultaneous measurements using two ion-selective electrodes showed a delay of the potassium efflux in comparison to the other ions that participate in the flg22 response. In the second approach, membrane potential measurements were performed while changing extracellular concentrations of protons, calcium, potassium or anions. Changing the anion gradient had the greatest impact on flg22 induced depolarization, suggestive of anion channel activation. Exudates analyses of flg22 treated leaves revealed that nitrate was the favored anion transported. Among many putative channel blocking agents tested, only lanthanum was identified to be potent in blocking the flg22 induced the cytosolic calcium rise, proton influx, and membrane potential depolarization. Since lanthanum represents a non-specific cation channel blocker, we favor to conclude that a calcium dependent activation of anion channels mediated membrane potential depolarization and consequently outward rectifying potassium channels. Future studies with double-barreled microelectrode voltage-clamp or external ion selective electrodes on intact guard cells may help to gain further information about the nature of ion channels in innate immunity or plant microbe interaction in general. Of course, all over the electrophysiological characterization of the multiple ion fluxes in innate immunity the next important step would be to discover the gene(s) coding for ion channels or transporters activated by non necrotic elicitors as flg22 in the innate immune response of plants.

Plant hormones act in a complex network where their pathways regulate and interact to control different mechanisms, such as development and stress responses. This crosstalk between hormones can be exploited by pathogens to suppress plant defense responses and thereby increase pathogen growth. Pseudomonas syringae pathogenicity is reliant on a Type III secretion system (TTSS) that acts as a specialized injection apparatus to deliver virulence proteins, known as type III effectors (TTEs), into the plant cell cytosol. In my work, I have screened hormone inducible promoter::GUS transgenic Arabidopsis thaliana lines against a P. syringae TTE library in order to identify TTEs involved in the perturbation of hormone signaling in planta. Through this screen I identified two P. syringae TTEs, HopAK1 and HopAL1, both belonging to the same bacterial strain P. syringae pv. maculicola ES4326. I found that HopAK1 can sensitize A. thaliana plants to auxin. On the other hand, HopAL1 activates auxin signaling. Monitoring of auxin signaling was done using transgenic DR5::GUS plants. Both TTEs render the plant susceptible to bacterial infection, highlighting a potential relationship between increased auxin signaling and virulence.

Plant hormones act in a complex network where their pathways regulate and interact to control different mechanisms, such as development and stress responses. This crosstalk between hormones can be exploited by pathogens to suppress plant defense responses and thereby increase pathogen growth. Pseudomonas syringae pathogenicity is reliant on a Type III secretion system (TTSS) that acts as a specialized injection apparatus to deliver virulence proteins, known as type III effectors (TTEs), into the plant cell cytosol. In my work, I have screened hormone inducible promoter::GUS transgenic Arabidopsis thaliana lines against a P. syringae TTE library in order to identify TTEs involved in the perturbation of hormone signaling in planta. Through this screen I identified two P. syringae TTEs, HopAK1 and HopAL1, both belonging to the same bacterial strain P. syringae pv. maculicola ES4326. I found that HopAK1 can sensitize A. thaliana plants to auxin. On the other hand, HopAL1 activates auxin signaling. Monitoring of auxin signaling was done using transgenic DR5::GUS plants. Both TTEs render the plant susceptible to bacterial infection, highlighting a potential relationship between increased auxin signaling and virulence.

In 2011 was conducted experimental plantings on land ZF Mendelu in the Lednice for determining the relative resistance of selected varieties of apricots, and to determine the potential substances to enhance resistance to P. syringae pv. syringae. The varieties were inoculated with strains FN3, Lmg1247 and CCM4073. In 2013 and 2014 were observed selected symptoms on plants, which was determined the level of relative resistance of each variety. As resistant varieties were determined 'Kuresia', 'Orangered', 'Bergeval' and 'Bergarouge'. As moderately susceptible varieties were determined 'Tardicot', 'Leskora', 'Aurora', 'Harogem', 'Pinkcot' and 'Sylvercot' on rootstock 'Waxva'. As susceptible varieties were determined 'Goldrich', 'Kioto', 'Bergeron' and 'Sylvercot' on rootstock 'Rubira'.

Submitted by Marco Antônio de Ramos Chagas (mchagas@ufv.br) on 2017-04-20T13:00:17Z No. of bitstreams: 1 texto completo.pdf: 327861 bytes, checksum: 10b3c4ac9c1fb002cc94c4da4da28d0e (MD5) / Made available in DSpace on 2017-04-20T13:00:17Z (GMT). No. of bitstreams: 1 texto completo.pdf: 327861 bytes, checksum: 10b3c4ac9c1fb002cc94c4da4da28d0e (MD5) Previous issue date: 2002-12-03 / Fundação de Amparo à Pesquisa do Estado de Minas Gerais / A busca de alimentos produzidos sob um sistema de manejo menos agressivo ao meio ambiente vem sendo adotado por um número cada vez maior de produtores. Entretanto, apesar de existirem diversos benefícios na redução ou até eliminação do uso de defensivos, a grande diversidade de doenças em tomateiro (Lycopersicon esculentum Mill.), capazes de limitar a produção, torna necessária a busca por alternativas viáveis, eficientes e tecnicamente comprovadas. Dentre os organismos mais estudados, bactérias têm sido relatadas como agentes de biocontrole capazes de atuar por meio de mecanismos como antibiose, parasitismo, competição e indução de resistência. O presente trabalho teve como objetivos selecionar bactérias do filoplano do tomateiro, baseado em uma estratégia de seleção in vivo, verificando se há um método de isolamento que permita obter antagonistas eficientes no controle da pinta-preta, causada por Alternaria solani, requeima por Phytophthora infestans, mancha-bacteriana pequena por Pseudomonas syringae pv. tomato e mancha-bacteriana por Xanthomonas vesicatoria. Objetivou ainda estudar a possibilidade dos mecanismos de antibiose e indução de resistência serem responsáveis pelo controle destas doenças e se testes de antibiose in vitro são adequados como critério de seleção. Caracterizar aspectos biológicos dos antagonistas que podem otimizar sua aplicação como agente de biocontrole. Determinar a quais produtos antimicrobianos os isolados são insensíveis, visando fornecer subsídios para o desenvolvimento de meios semi-seletivos e estudos de dinâmica populacional. Verificar sua compatibilidade com antibióticos e fungicidas registrados para o controle de enfermidades do tomateiro, a fim de inseri-lo no sistema de manejo integrado e estudar a eficiência de antagonistas selecionados em condições de campo. Os resultados demonstram que, em folíolos mais jovens, os métodos de isolamento que visam obter bactérias da população total e da superfície do filoplano, foram os que permitiram obter a maioria dos antagonistas. O único obtido de folíolos mais velhos foi proveniente da população capaz de habitar sítios protegidos do filoplano e/ou resistir a fatores de estresse. Não se observou relação entre características biológicas dos antagonistas e dos patógenos testados. Nos testes de antibiose com os antagonistas selecionados, o isolado UFV-STB 6 foi capaz de produzir compostos voláteis e inibir a germinação de cistos de Phytophthora infestans, o que possivelmente deve estar envolvido no controle da requeima. O isolado UFV-IEA 6 produziu quitinase, havendo uma tendência em reduzir a taxa de crescimento de Alternaria solani por compostos voláteis. Ficou demonstrado que os testes de antibiose in vitro são inadequados como critério para seleção de agentes de biocontrole do filoplano de tomateiro. A caracterização dos melhores antagonistas demonstrou que três são bactérias Gram-positivas, em forma de bastonete, e uma Gram-negativa, pleiomórfica. Dentre as Gram-positivas todas são anaeróbias facultativas e uma forma endósporos. Nenhum antagonista foi capaz de causar reação de hipersensibilidade (HR) em fumo e produzir pigmento fluorescente in vitro. Os períodos de geração calculados a partir das curvas de crescimento revelaram que três isolados são capazes de se multiplicar rapidamente em meio de cultura, o que é uma característica desejável. Os resultados obtidos a partir dos antibiogramas, mostraram que existem antibióticos que podem ser utilizados para elaboração de meios semi-seletivos, adequados a cada antagonista e os testes de compatibilidade com antibióticos e fungicidas utilizados na cultura do tomateiro revelaram que os antagonistas podem ser expostos aos fungicidas benomyl, enxofre, dimetomorph e tiofanato-metílico. Verificou-se também a inadequação de se utilizarem compostos antimicrobianos em meio de cultura para isolamento de agentes bacterianos de controle biológico, uma vez que os antagonistas selecionados foram sensíveis à maioria dos produtos testados. Os testes com as enzimas indicadoras do estado de indução de resistência, β-1,3-glucanases, Fenilalanina amônia-liase (PAL), Peroxidases (PO), Polifenoloxidases (PPO) e Lipoxigenases (LOX), indicaram que o isolado UFV-IEA 6 foi capaz de promover aumento significativo na atividade das PO, evidenciando a possibilidade do antagonista agir como indutor de resistência. Esse parece ser o primeiro caso que se tem conhecimento de uma bactéria não fitopatogênica do filoplano induzindo resistência na mesma cultura de onde foi obtida. Os testes com os dois antagonistas em condições de campo demonstraram que UFV-STB 6 foi o mais eficiente em reduzir a severidade da requeima no terços médio e superior das plantas, enquanto UFV-IEA 6, somente no terço superior. Houve tendência na redução do progresso da septoriose por UFV-STB 6 e capacidade em diminuir o número de frutos com sintomas de requeima. Os resultados demonstram o potencial de uso dos agentes de biocontrole selecionados para as doenças da parte aérea de tomateiro estudadas. / Farmers are increasingly adapting environmentally less aggressive management systems for food production and there are many benefits in reducing or even eliminating pesticide use. Due to a large number of production limiting diseases on tomato (Lycopersicon esculentum), it is desirable to find technically viable and proven alternatives for their control. Among the microorganisms, bacteria have been reported as biocontrol agents capable of acting through antibiosis, parasitism, competition and induced resistance. The present study aimed at selecting the tomato phylloplane bacteria, based on in vivo isolation strategy, and to determine if this method permits obtaining efficient antagonists to control Alternaria solani leaf spot, Phytophthora infestans blight, small bacterial leaf spot caused by Pseudomonas syringe pv tomato, and bacterial leaf spot caused by Xanthomonas vesicatoria. The study also aimed at determining mechanisms of action, such as antibiosis and induced resistance, involved in disease control, and to determine if the antibiosis tests are sufficient selection criteria. The study also included biological characterization of the antagonists that may optimize their use. To help develop selective or semi-selective media for population dynamic studies, insensitivity of selected isolates to some antimicrobial compounds was also determined. The compatibility of select antagonists with antibiotics and fungicides registered for control of tomato diseases was elucidated so that the antagonist can be inserted in the integrated management. Field studies were done to determine the efficiency of select antagonists. The isolation method that obtain total bacterial population from the phylloplane of the young leaflets permitted obtaining maximum number of antagonists. The only one isolate obtained from the older leaflets originated from the population capable of inhabiting protected sites of phylloplane and/or that resist stress factors. There was no relation between biological characteristics of the antagonists and of the pathogen tested. In the antibiosis testes, the isolate UFV-STB 6 produced volatile compounds that inhibited germination of P. infestance cyst and may be involved in the control of blight. The isolate UFV-IEA 6 produced chitinase and showed a tendency to reduce A. solani growth by the volatile compounds. In vitro antibiosis testes were inadequate criteria to select biocontrol agents from tomato phylloplane. The characterization of promising antagonists showed that three were Gram positive bacilli and one was gram negative pleiomorphic bacteria. Among the Gram positives all were facultative anaerobes and the one formed endospores. None of the antagonists caused hypersensitive reaction (HR) in tobacco, and did not produce fluorescent pigment in vitro. The generation period calculated from the growth curve revealed that three isolates are capable of multiplying rapidly in the culture media, which is a desirable characteristic. The antibiograms showed that there are antibiotics that can be used for elaboration of semi-selective media for each of antagonists and the compatibility testes with antibiotics and fungicides used on tomato crop revealed that the antagonists can be exposed to fungicides such as benomyl, sulfur, dimethomorph and thiophante-methyl. Many antimicrobial compounds were inhibitory to the selecte antagonists in culture media used for isolation of bacterial biocontrol agents, therefore were inadequate for use in selective media. The analysis of enzymes involved in induced resistance, like -1,3-gluconase, phenylalanine ammonia lyase (PAL), peroxidase (PO), polyphenol oxidase (PPO) and lipoxigenase (LOX), showed that the isolate UFV-IEA 6 was capable of increasing PO activity, showing the possibility of being a resistance inducer . This appears to be the first case of a non-pathogenic phylloplane bacterium inducing resistance in a plant of origin. The field testes with two antagonists, UFV-STB 6 was more efficient in reducing the blight severity in the middle and upper third of the plant, while UFV-IEA 6 only in the upper third. The latter isolate also showed a tendency for reducing the Septoria leaf spot progress and the number of fruits with the blight symptoms. The results showed these isolates have the potential of use to control tomato diseases of aerial parts. / Tese importada do Alexandria

Doctor of Philosophy / Department of Plant Pathology / Xiaoyan Tang / P. syringae is a group of bacterial phytopathogens that can infect a wide variety of plants. These bacteria rely on the type III secretion system (TTSS) to deliver effectors into plant cells for infection. The TTSS genes, that encode the TTSS apparatus and the effectors, are repressed when bacteria grow in nutrient rich media but are strongly induced in the plants and in minimal medium (MM). Plant cutin monomers appear to negatively regulate the P. syringae TTSS genes. It is poorly understood how bacteria sense the environmental signals to regulate the TTSS genes. By genetic screen, four sets of transposon insertion mutants displaying aberrant TTSS gene expression were isolated: KB and fin mutants derepress the TTSS genes in rich medium KB and in the presence of a cutin monomer precursor in MM, respectively; min and pin mutants are defective in induction of TTSS genes in MM and in plants, respectively. A putative two-component sensor histidine kinase, RohS, is identified to be required for the induction of avrPto-LUC in MM and in plants. The rohS gene is in an operon containing a two-component response regulator gene rohR. Mutation of rohS in P. s. phaseolicola and P. s. tomato reduced the bacterial pathogenicity on hosts and HR-inducing activity on non-hosts. Our results suggested that RohS acts upstream of HrpR/HrpS. The phosphorylated RohR represses TTSS genes. It is likely that RohS acts as phosphatase of RohR in the TTSS-inducing conditions, and subsequently derepresses TTSS genes. Simple sugars such as glucose, sucrose and fructose are known to be inducers of the TTSS genes. Isolation of four min mutants defective in fructose-uptake enabled us to study if sugars serve as extracellular signals or as essential nutrients. Our results suggest that fructose acts as an essential nutrient for the activation of type III genes. These mutants slightly compromised induction of avrPto promoter in Arabidopsis and pathogenicity on the host bean plant, but displayed normal HR elicitation on non-host plant tobacco. The reduced pathogenicity suggested that exploitation of fructose from the host tissue is an important means for pathogenesis of P. s. phaseolicola.

Doctor of Philosophy / Department of Plant Pathology / Jianmin Zhou / Plants activate innate immune responses or innate immunity upon pathogen infection. There are two types of plant innate immunity: PAMP-triggered innate immunity (PTI) and effector-triggered innate immunity (ETI). The molecular basis for ETI has been well documented. However, the study on PTI and its interplay with pathogen virulence is in its infancy. My research focuses on the interplay between PTI and bacterial virulence in Pseudomonas-Arabidopsis interactions. NHO1, a gene required for nonhost resistance to Pseudomonas syringae, encodes for the 3-glycerol kinase in Arabidopsis genome. NHO1 functions, at least in part, by depriving glycerol from nonhost bacteria cells. NHO1 is induced by a well-known bacteria PAMP flg22. The induction of NHO1 correlates well with the resistance against Pseudomonas syringae pv. tabaci because a mutant strain of P. s. pv. tabaci deficient in NHO1 induction gains partial virulence on Arabidopsis plants. P. s. pv. tomato strain DC3000 induces transient NHO1 expression that is suppressed in a type III secrection system-dependent manner. Using protoplast assay, nine DC3000 effectors that are able to suppress NHO1 were identified. One of them, HopAI1, induces leaf chlorosis and helps nonpathogenic bacterial growth when expressed in Arabidopsis plants, suggesting that HopAI1 has virulence activity in planta. To study AvrB virulence activity in Arabidopsis plants, one mutant compromised in AvrB-specific RAR2.6 induction has been characterized in detail. rrb3 is more susceptible to a nonhost bacteria P. s. pv. tabaci strain 6505, a virulent bacteria P. s. pv. tomato strain DC3000 and an avirulent bacteria strain DC3000 (avrB). The mutant allele rrb3 carries a point mutation at the end of RAR1 CHORD II domain. RRB3 (RAR1), together with NDR1, is involved in the type II nonhost resistance to P. s. pv. tabaci but not in the type I nonhost resistance to P. s. pv. phaseolicola. RAR1 participates in basal resistance against DC3000 by antagonizing COI1 activity. AvrB targets RAR1 to trigger AvrB-dependent leaf chlorosis and enhanced bacterial growth. The AvrB-dependent enhanced bacterial growth but not leaf chlorosis requires COI1, suggesting that AvrB targets JA signaling pathway to promote parasitism.

The aim of this diploma thesis is determination of the influence of deficient nutrition in combination of Pseudomonas syringae pv. tomato infection on tomato (Solanum lycopersicum L.) growth and development. In hydroponic cultivation experiment, tomato variety Darinka was cultivated in solutions without N, P, K, Ca, Mg and in variant with all nutrition (control variant). The dry matter of root and stem was weighed and root length, density and electrical capacitance were set. The content of nutrition in plants was also assessed. The level of infection was determined in 1st term, the highest level had plants with insufficient of Ca and P. High reduction of root and stem dry matter was found in Ca, N, P and Mg deficient plants. The low root electrical capacitance, length and density was determined in plants with Ca, N a P deficiency within infected group and in Ca and N deficient plants within noninfected group. Bacterial infection caused the reduction of all observing parameters in contrast to the plants from noninfected group. The antagonism and synergism between the elements were also showed.