Adeno-associated virus type 2 (AAV-2) integrates preferentially into a defined site on human chromosome 19, and has been developed as a gene therapy vector. We propose to use this unique recombination event for site-specific integration of transgenes in plants. This strategy would alleviate problems associated with current plant transformation methods that integrate transgenes randomly. The AAV-2 gene encoding the enzyme that catalyzes the insertion (rep78) was introduced into Arabidopsis thaliana via Agrobacterium-mediated transformation. PCR and sequence analysis confirmed the presence of rep78 in two plant lines. RT-PCR demonstrated rep78 transcription in one plant line, but protein could not be detected in either line. / Master of Science

Background: The EXO (EXORDIUM) gene was identified as a potential mediator of brassinosteroid (BR)-promoted growth. It is part of a gene family with eight members in Arabidopsis. EXO gene expression is under control of BR, and EXO overexpression promotes shoot and root growth. In this study, the consequences of loss of EXO function are described. Results: The exo loss of function mutant showed diminished leaf and root growth and reduced biomass production. Light and scanning electron microscopy analyses revealed that impaired leaf growth is due to reduced cell expansion. Epidermis, palisade, and spongy parenchyma cells were smaller in comparison to the wild-type. The exo mutant showed reduced brassinolide-induced cotyledon and hypocotyl growth. In contrast, exo roots were significantly more sensitive to the inhibitory effect of synthetic brassinolide. Apart from reduced growth, exo did not show severe morphological abnormalities. Gene expression analyses of leaf material identified genes that showed robust EXO-dependent expression. Growth-related genes such as WAK1, EXP5, and KCS1, and genes involved in primary and secondary metabolism showed weaker expression in exo than in wild-type plants. However, the vast majority of BR-regulated genes were normally expressed in exo. HA- and GFP-tagged EXO proteins were targeted to the apoplast. Conclusion: The EXO gene is essential for cell expansion in leaves. Gene expression patterns and growth assays suggest that EXO mediates BR-induced leaf growth. However, EXO does not control BR-levels or BR-sensitivity in the shoot. EXO presumably is involved in a signalling process which coordinates BR-responses with environmental or developmental signals. The hypersensitivity of exo roots to BR suggests that EXO plays a diverse role in the control of BR responses in the root.

A novel strategy for site-specific DNA transformation of plants has been proposed and the first component of the system developed. The proposed method overcomes the limitations of current techniques by providing a specific integration site for the insertion of transgenes using features of the adeno-associated virus (AAV) life cycle. In the absence of helper virus, AAV integrates into a specific location on human chromosome 19, the AAVS1 locus. The sequence for AAV integration was introduced into the model plant Arabidopsis thaliana using Agrobacterium tumefaciens-mediated transformation. A portion of the human AAVS1 sequence, including the Rep binding site (RBS) and terminal resolution site (TRS), was cloned between T-DNA borders of the Agrobacterium Ti plasmid. The reporter gene, b-glucuronidase (GUS) was inserted proximal to AAVS1 in the plasmid for use in screening for the presence of T-DNA. In addition, it will serve as an indicator of the expression level expected for transgene inserted into AAVS1 by recombinant AAV. PCR amplification, dideoxy sequencing, GUS expression assays and genomic Southern blots were performed to examine putative transgenic plants for the presence of the AAVS1 sequence. / Master of Science

No description available.

The Rosaceae contains many important commercially grown fruit crops. No comprehensive genomics platform is currently under development for fruit crops, giving functional genomics studies with wild strawberry (Fragaria vesca L.) the potential of identifying genes important in fruit crops. Fragaria vesca has a small genome size compared to the cultivated strawberry, Fragaria à ananassa Duch. (164 vs. 600 Mbp per 1C nucleus). This feature, in addition to a short life cycle (12-16 weeks) and small plant size make F. vesca a good candidate for a model plant for genetic and molecular studies. The specific objective of this work was to develop an efficient high-throughput Agrobacterium-mediated transformation protocol to generate an insertional mutant population to support the justification of F. vesca as a model organism for rosaceous crops. The transformation techniques described by Alsheikh et al. (2002) and Oosumi et al. (2005) were modified and applied to a range of germplasm obtained from the USDA National Germplasm Repository. We found that the modifications made to the Alsheikh protocol were unsuccessful when applied to our germplasm. With the Oosumi et al. (2005) protocol, transformation efficiencies ranging from 11 to 100% were obtained for two accessions when explants were exposed to varying durations on TDZ containing medium during shoot regeneration. The transformation efficiency was given as the mean number of GFP+ plants obtained per primary explant cultured. Multiplex PCR, for amplification of the hptII and GFP genes, was performed on a random sample of GFP+ plants to verify insertion of the T-DNA. The statistical power of our experiment was insufficient to detect treatment effect but based on our findings the transformation efficiencies were high enough to justify PI 551572 for use in the high throughput transformations that are required to generate a population of insertional mutants large enough for gene discovery in F. vesca. / Master of Science

Pathogen derived resistance (PDR) is a recent breakthrough where plant hosts can be made to be resistant to viral infections through transformation with conserved viral genes. Given the severity of Tospovirus diseases worldwide (particularly in tomato), PDR has the potential to garner large yield returns where pathogen populations have overcome the established resistance. Tomato breeding lines FLA7804, FLA8044, and the research line MP1 were used in transformation experiments with potions of the Tomato spotted wilt virus (TSWV) N-gene, and two other chimerical viral nucleocapsid gene constructs from, Impatiens necrotic spot virus (INSV), and Groundnut ringspot virus (GRSV). We conducted 19 independent transformations consisting of 300 to 700 14-day old whole cotyledons each for a total number of approximately 9,000 potentially transformed explants. Of those, approximately 6,300 explants failed to produce regenerants, 2,419 explants underwent abnormal development on elongation media, 187 failed to root, and 215 plants to be characterized genetically. Of the 215 plants, 9 were from FLA 7804, 96 from FLA 8044, and 110 from MP1. Both PCR and Southern blot hybridization analysis later confirmed that none of the 215 plants were transgenic. Opposite to tomato, we were able to transform Arabidopsis thaliana ecotype wassilewskija (Ws) via floral dip with the above listed constructs demonstrating that constructs were not deleterious within a plant once fully introgressed. Sixteen independent transformants in the T0 generation resulted from 19,000 germinated seed from three dipped plants resulting in a total transformation rate of 0.08%. Of the 1,000 T1 seed germinated on kanamycin media from each of the 16 putative Arabidopsis plants transformed with the construct containing elements of the N-gene from all three of the aforementioned tospoviruses, four populations exhibited simple Mendelian inheritance of the transgene. DNA walking analysis yielded amplification of the unknown region outside the nptII region of the insert for three of the four remaining transformants, which was subsequently sequenced and mapped to chromosomes 1, 3, and 4. There were 25 T1 individuals selected from each population and transferred to soil for DNA extraction and zygosity determination. Homozygous T2 seed was collected for future resistance studies.

No description available.

No description available.

The salicinoids are phenolic glycosides (PGs) characteristic of the Salicaceae family and are known defenses against insect herbivory. Common examples are salicin, salicortin, tremuloidin, and tremulacin, which accumulate to high concentrations in the leaves and bark of willows and poplars. Despite their important role in plant defense, their biosynthetic pathway is not known, although recent work has suggested that benzyl benzoate acts as a possible biosynthetic intermediate. We identified three candidate genes encoding BAHD-type acyltransferases that are predicted to produce benzylated secondary metabolites, named PtACT47, PtACT49, and PtACT54. Expression of PtACT47 and PtACT49 generally correlated with PG content in a variety of tissues and organs of wild type hybrid poplar plants. This correlation was also found in transgenic hybrid poplar where PG content varied with the level of expression of the condensed tannin regulator MYB134 transcript. In these plants, a suppression of PtACT47 and PtACT49 expression was correlated with lower PG content. In contrast, PtACT54 exhibited very low expression in all tissues tested, and this level of expression was not affected in MYB134 plants. In order to better understand their possible biochemical functions, cDNA cloning, heterologous expression, and in vitro functional characterization was performed on these three BAHD acyltransferases. Recombinant PtACT47 exhibited a low substrate selectivity and could utilize acetyl-CoA, benzoyl-CoA, and cinnamoyl-CoA as acyl donors with a variety of alcohols as acyl acceptors. This enzyme showed the greatest Km/Kcat ratio (45.8 nM-1 sec-1) and lowest Km values (45.1 µM) with benzoyl-CoA and salicyl alcohol, and was named benzoyl-CoA:salicyl alcohol O-benzoyltransferase (PtSABT). Recombinant PtACT49 utilized a narrower range of substrates, specifically benzoyl-CoA and acetyl-CoA and a limited number of alcohols. Its highest Km/Kcat (31.8 nM-1 sec-1) and lowest Km (55.3 µM) was observed for benzoyl-CoA and benzyl alcohol, and it was named benzoyl-CoA:benzyl alcohol O-benzoyltransferase (PtBEBT). Both enzymes were also capable of synthesizing plant volatile alcohol esters at trace levels, for example hexenyl benzoate. Recombinant PtACT54 shares low sequence identity with PtSABT (52.3%) and PtBEBT (52.5%) and exhibited only moderate BEBT-like properties. PtSABT and PtBEBT appear to be paralogs based on their high sequence identity (90.6%) and closely related yet distinct biochemical functions. They likely arose from gene duplication and subsequent functional diversification possibly by neofunctionalization. Wounding experiments showed that abiotic damage stimulated the synthesis of specific PGs, notably salicin and salicortin within 24-48hrs. This was accompanied by a proportional increase in the expression of PtSABT and PtBEBT. Furthermore, experiments using transgenic RNAi lines with knock-down suppression of PtBEBT, and PtSABT, and both genes simultaneously, provided the first direct evidence that BAHD acyltransferases are important in PG production. PtSABT suppression, both individually and in the double knock-down suppression, significantly lowered salicortin content, particularly in mature leaves. However, a reduced level of PtBEBT expression did not have a significant effect on the PGs measured. This could indicate that BEBT-like activity may be a shared function among closely related BAHDs. The suppression of multiple BEBT-like genes may be necessary to further delineate their functions. / Graduate / rjchedgy@uvic.ca

When tomato Craigella is infected with Verticillium dahliae Dvd-E6 (Dvd-E6), a tolerant state is induced with substantial pathogen load, but few symptoms. Unexpectedly, these plants are more robust and taller with Dvd-E6 behaving as an endophyte. Some endophytes can protect plants from virulent pathogens. This research was undertaken to improve understanding of the cellular and molecular nature of Verticillium tolerance in tomato, especially whether infection by Dvd-E6 can protect Craigella from virulent V. dahliae, race 1 (Vd1). To permit mixed infection experiments a restriction fragment length polymorphism (RFLP)-based assay was developed and used for differentiating Dvd-E6 from Vd1, when present in mixed infections. The results suggested that protection involves molecular interplay between Dvd-E6 and Vd1 in susceptible Craigella (CS) tomatoes, resulting in restricted Vd1 colonization. Further studies showed a dramatic reduction of Vd1 spores and mycelia. To examine genetic changes that account for these biological changes, a customized DNA chip (TVR) was used to analyze defense gene mRNA levels. The defense gene response was categorized into four groups. Group 1 was characterized by strong induction of defense genes followed by suppression. However, Vd1-induced gene suppression was blocked by Dvd-E6 in mixed infections. These genes included some transcription factors and PR proteins such as class IV chitinases and beta glucanases which are known to target fungal spores and mycelia. Experiments also were repeated with a Craigella resistant (CR) isoline containing a fully active Ve locus (Ve1+ and Ve2+). The biological results showed that the presence of the Ve1+ allele resulted in restricted Vd1 colonization and, in a mixed infection with Dvd-E6, Vd1 was completely eliminated from the plant stem. Surprisingly, there was no significant increase in defense gene mRNAs. Rather, elevated basal levels of defense gene products appeared sufficient to combat pathogen attack. To investigate functional effects of the genetic changes observed, an inducible RNAi knockdown vector for a defense gene (TUS15G8) with unknown function (pMW4-TUS15G8) as well as the Ve2 resistance gene (pMW-Ve2) was prepared as a initial step for future transformation analyses. Taken together the results reveal intriguing but complex biological and molecular changes in mixed infections, which remain a basis for future experiments and potential agricultural benefits. / Canadian Commonwealth Scholarship and Fellowship Plan