A transgenic <i>Arabidopsis</i> line containing a chimeric <i>PR-1::luciferase (LUC)</i> reporter gene was subjected to mutagenesis with activation tags. Screening of lines via high throughput LUC imaging identified a number of dominant <i>Arabidopsis</i> mutants that exhibited enhanced <i>PR-1</i> gene expression. Here we report the characterisation of one of these mutants, designated activated disease resistance (<i>adr</i>) 1. This line showed constitutive expression of a number of key defence marker genes and accumulated salicylic acid, but not ethylene or jasmonic acid. Furthermore, <i>adr1</i> plants exhibited resistance against the biotrophic pathogen <i>Peronospora parasitica</i> and <i>Erysiphe cichoracearum</i> but not the necrotrophic fungus <i>Botrytis cineria.</i> Analysis of a series of <i>adr1</i> double mutants suggested that <i>ADR1-</i>mediated resistance against <i>P. parasitica</i> was SA-dependent, while resistance against <i>E. cichoracearum</i> was both SA-dependent and partially NPR1-dependent. The controlled, transient expression of <i>ADR1</i> conveyed striking disease resistance in the absence of yield penalty, highlighting the potential utility of this gene in crop protection. Homologous genes were uncovered in many phylogenetically distant and agronomically important plant species; their sequence analysis revealed a number of consensus motifs unique and distinctive for the ADR1 family. Furthermore, we show that either constitutive or conditional enhanced expression of <i>ADR1</i> conferred significant drought tolerance. Cross-tolerance was not a characteristic of <i>adr1</i> plants; rather they showed increased sensitivity to thermal and salinity stress.  Hence, <i>ADR1</i> activated signalling may antagonise some stress responses. Additionally, a large activation tagged population was screened in order to isolate novel mutants altered in disease susceptibility.  Here we report the characterisation of one mutant, designated activated disease susceptibility (<i>ads</i>) 1. This line was confirmed to concurrently exhibit increased susceptibility to hemi-biotrophic, necrotrophic and non-host pathogens.

White clover is an allotetraploid legume with a genome size of ca 960 Mb and is widely used in Irish grasslands to improve the nutritional value of the forage by increasing the relative amounts of nitrogen present. White clover is closely related to Medicago truncatula, the diploid (genome size of ca 500 Mb) model legume chosen to study the symbiotic genetic programmes of plants and facilitate the genetics and breeding of important legume crops. This thesis describes the construction of a genetic map of a white clover mapping population composed of 94 F1 progeny bred in the Institute of Grassland and Environmental Research (UK) from parents S1S4 and R3R4. The genetic map was constructed using amplified fragment length polymorphism markers and white clover microsatellite markers from previously published white clover maps. The thesis also details a glasshouse and field based phenotypic analysis carried out on morphological traits which allowed quantitative trait loci (QTL) to be detected on the genetic linkage map of white clover. Due to the high correlation between the traits measured, both conservation of QTLs across environments and co-localisation of QTLs for related traits were observed in this study. A BAC library of one of the family parents, R3R4, was constructed using pIndigo BAC-5, consisting of over 37,000 clones with an average insert size of 85 Kb, representing a threefold genome coverage. A preliminary sequence analysis was carried out where 700 BAC clones were sequenced on both ends. Results showed that over 50% of the BAC-ends had a correspondence with the Medicago genome sequence; however only 16 of the BAC-end sequence pairs had homology within a span of 20 to 200 Kb in M. truncatula. The level of synteny between white clover and M. truncatula was assessed by comparative structural genomics, where five BAC clones of the white clover library were sequenced to sixfold coverage and their sequences were compared to the corresponding M. truncatula sequences.

Ascorbate peroxidase (EC: 1.11.1.11; APX) scavenges hydrogen peroxide. Hydrogen peroxide is a reactive oxygen intermediate (ROI) that is generated in numerous cellular reactions and is linked to signalling pathways associated with a diversity of environmental stimuli. If the production of hydrogen peroxide exceeds the capacity of scavenging systems to remove it, this ROI will accumulate and photooxidative stress may result. There are five known members of the APX gene family in Arabidopsis. This project focused on the role and regulation of the APX2 gene. In the Arabidopsis ecotype Columbia, expression of this gene is not detectable in the absence of stress. However, when leaves are exposed to high light or wounding, APX2 gene expression is rapidly, but transiently induced. Karpinski et al. (1999) proposed that APX2 gene expression is associated with acclimating Arabidopsis plants to photooxidative stress. The aim of this project was to isolate mutants with deregulated APX2 gene expression to provide an insight into how this gene is regulated and what effect altering its expression has on the response to photooxidative stress. A mutagenesiss creenw as developedt o isolateA rabidopsism utantst hat expressedth eA PX2 genew ithout high light or wound treatments.T o facilitate this screen,a transgenicl ine with a luciferaser eporter genew as mutagenisedT. hirty four thousandM 2 plantsw ere screenedfo r luciferasea ctivity undern on-stressc onditions.T wo allelic, recessivem utantsw ere identified that were alteredi n both luciferasea ctivity ande ndogenousA PX2 genee xpression;t hesew ere called regulators of ascorbatep eroxidase (rap]). The abundanceo f APX2 RNA in non-stressedm utant rosettes was not as high as that in stress treated leaves. Imaging of luciferase activity indicated that this expression varied between leaves. As in wildtype plants, APX2 gene expression was associated with the vascular system. rap] rosettesh ave alterede xpressiono f genest hat encodeo there nzymesa ssociatedw ith antioxidant defence, besides APX2. These genes encode isoforms that scavenge superoxide radicals (superoxided ismutase)a ndr educeo xidised forms of ascorbate( monodehydroascorbate and dehydroascorbatree ductases)T. he mutantsh ave approximatelyo ne third of the glutathione contento f wildtype rosettesT. his is consistentw ith the finding that APX2 genee xpressioni s impaired in Arabidopsis leaves treated with this thiol (Karpinski et al. 1997). Glutathione is an antioxidant and plants in which antioxidant defences are compromised might be expected to accumulater eactiveo xygen speciess ucha s hydrogenp eroxide.I ncreasedh ydrogen peroxide content inducesa low level of APX2 genee xpression( Karpinski et al. 1997),c omparablet o that detectedi n rap] rosettesH. owever, total foliar hydrogenp eroxidec oncentrationw as not detectably altered in the mutants. In response to high light and wounding, rapl rosettes accumulated higher concentrations of APX2 transcripts than wildtype plants. However, rapid fluorescence measurements indicated that there was no difference in the sensitivity of mutant rosettes to a high light stress. A numbero f Arabidopsise cotypesw ere identified that expressedth e APX2 geneu nder conditions that did not induce expression in Columbia plants.

Genetic maps were produced from wide crosses between the garden pea Pisum sativum and the cultivated species P. abyssinicum, cultivation of which is confmed to North-east Africa and Yemen. Crosses were made in two directions: with P. abyssinicum as the female parent in ll2202 (P. abyssinicum) x ll2822 (P. sativum), and as the male parent in Kite (P. sativum) x ll2 (P. abyssinicum). Parallel linkage maps were produced for the two populations. 454 markers were mapped in the ll2202 x ll2822 F7 population, and 252 in the Kite x ll2 F6 population, using predominantly SSR (simple sequence repeat) and SSAP (sequence-specific amplification polymorphism) markers. 152 markers are shared between linkage maps; this figure represents more than 50% of the mapped markers derived from the primer combinations that were used on both populations. A number of novel loci were associated with segregating traits derived from both cross parents. Analysis in the ll2202 x ll2822 population found strong partial resistance to infection by downy mildew (Peronospora viciae f. sp.pisi), in which 52% of trait variance was explained by a single locus on linkage group I. This source of resistance is derived from the P. sativum parent. Significant segregation distortion affected approximately half of the markers used in the linkage maps; segregation ratios were found to be biased in favour of maternal alleles in both populations, which may represent a fonn of partial reproductive isolation between P. abyssinicum and P. sativum. Combined with observed transgressive segregation of domestication traits in the wide crosses, this suggests that these taxa do not have a shared domestication history.

Japanese Knotweed s.l. comprises taxa from the genus Fallopia section Reynoutria, and were introduced to Britain from Asia during the 19th century. The hybrids are believed to have arisen since the introduction of the parental species. Inter-simple-sequence-repeat (ISSR) PCR was used to determine genotypes to examine the potential for sexual reproduction of F. x bohemica in Britain. At one site in Wales the distribution of the two parents and the resultant hybrid offspring were mapped, their genotypes assessed, and the relationships between the genotypes discussed. Evidence was found that both clonal spread and sexual reproduction play a role in the distribution of these plants. Twenty-six genotypes of established hexaploid and two of octoploid F. x bohemica were detected, indicative of continuous new recruitment to the population. Three locations in Britain where both male-fertile and male-sterile tetraploid hybrids are found were analysed for both chloroplast haplotype and genotype. Chloroplast haplotypes were determined by RFLP-PCR analysis of the chloroplast region trnC-trnD, and used to identify the direction of the cross that produced the F. x bohemica. Hybridisation was shown to occur in both directions. In total, ten different genotypes of established tetraploid F. x bohemica were detected, with no common genotype found between the different sites. Genetic diversity among British F. sachalinensis was examined. Most were found to be one of two genotypes, either a widespread male-fertile, or a widespread male-sterile clone. A molecular biogeographical study of F. japonica and F. sachalinensis in Japan was undertaken using PCR RFLPs of six chloroplast regions, trnK¹-trnK², trnC-trnD, trnF-trnV, trnH-trnK, trnD-trnT, and trnM-rbcL. The probable region of the source of the introduced material was identified. Additionally a sub-set of the plants was sequenced to better understand the relationships between the native taxa. To complement the molecular analysis, morphological and cytological investigations were also conducted.

Two species, Solanum commersonii Dun. and S. acaule Bitt., have been investigated. ii The two subspecies of S. commersonii, commersonii and malmeanum (Bitt.) Hawkes et Hjerting, have diploid and triploid forms. There are reciprocal differences between subspecies in diploid-diploid crosses, and between levels of ploidy in diploid-tetraploid crosses. Diploidtetraploid crosses produce mostly triploids and in this S. commersonii differs from other species. The selfincompatibility of the diploids breaks down in the tetraploids. In subsp. commersonii 'conventional' triploids are considered to be autopolyploids, and 'anomalous' triploids to be intersubspecific hybrids. Triploid cytotypes of subsp. malmeanum are probably autopolyploids. Diploid hybrids between the subspecies are also likely to be formed. Hybridization between S. commersonii and S. chacoense Bitt. is probably rare. S. acaule has three tetraploid and one hexaploid subspecies which are all probably segmental allopolyploids. The tetraploid subsp. aemulans (Bitt. et Wittm.) Hawkes et Hjerting is considered to be most closely related to other species; an alternative hypothesis is proposed for its origin. Attempts to obtain dihaploids of the tetraploid subspecies using diploid and autotetraploid pollinators, and from polyembryonic hybrid seeds have been unsuccessful. Previously unrecorded crosses of S. acaule with other species are reported. Embryological studies have been carried out in S. acaule, and embryo culture techniques developed. Polyembryony has been found in several taxa, and its occurrence in the tuber-bearing Solanums is reviewed.

The history is briefly reviewed. Biparental plastid inheritance is compared from several species. The hybrid lines of uncertain type II cultivars are selfed, and crossed with two type I testers, green Dolly Varden and W1A, to obtain hybrids. These are now crossed with white Flower of Spring, as source of mutant plastids, and the embryos scored. The three hybrids are all different, one is double heterozygote, <B>Pr1pr1, Pr2pr2</B> and the other two are single heterozygote for opposite genes, <B>Pr1Pr1, Pr2pr2 </B>and <B>Pr1pr1, Pr2Pr2</B>. From one hybrid, a single true-breeding double dominant <B>Pr1Pr1, Pr2Pr2</B> is raised. From many single heterozygotes, the male plastids are transmitted with high frequency, although with others the female plastids are favoured. The analysis confirms the importance of the two genes <B>Pr1 </B>and <B>Pr2</B> controlling biparental plastid inheritance, and in particular the value of the two testers in isolating all type IIs. Five white-over-green (variegated) cultivars (Dolly Varden, J.C. Mappin, Miss Burdett-Coutts, Flower of Spring and Frank Headley) were tested as the male parents (pollinators) with five different green females. The two type II mutants, Flower of Spring and J.C. Mappin are transmitted alike, but the plasmid of the other three, are significantly different. Dolly Varden is the most successful transmitter of white plastids from the male. The inheritance of flower colour is reviewed. The red and non-red flower colour genes fit expectations.

No description available.

No description available.

No description available.