Condensed tannins are wide-spread polyphenols with diverse ecological functions, including defense against herbivores and microbial pathogens. In poplar, condensed tannin synthesis is induced by a variety of biotic and abiotic stresses. The objective of this study was to determine the function of the R2R3 MYB transcription factor MYB115 in the regulation of condensed tannin synthesis. MYB115 was shown to be induced by wounding along with tannin biosynthetic genes and shows sequence similarity to characterized regulators of tannin synthesis in grape and persimmon suggesting that it functions in the regulation of condensed tannin synthesis. To analyze the function of MYB115, transgenic plants overexpressing MYB115 were generated and showed enhanced accumulation of condensed tannins and higher expression of flavonoid biosynthetic genes involved in condensed tannin biosynthesis compared to wild-type control plants. In promoter activation assays, MYB115 activated the promoter of a tannin-specific biosynthetic enzyme, anthocyanidin reductase. This suggests that MYB115 acts as a regulator of condensed tannin synthesis. MYB115 overexpressors showed additional changes to phenolic metabolism, including changes in levels of phenolic glycosides and hydroxycinnamic acids. These results indicate an important role of MYB115 in the regulation of the condensed tannin pathway in poplar. / Graduate / 0817 / 0307 / 0487 / frankla@uvic.ca

The relationship between an organism’s genome, developmental stage, and environment is complex. The aim of the research presented herein was to provide experimental evidence to contribute to the annotation of the P. trichocarpa genome and to test two major hypotheses addressing the interaction between drought and time of day in A. thaliana and in two hybrid Populus clones. In order to generate data to address these aims, three separate experiments were undertaken. First, all members of the R2R3-MYB family of transcription factors in the P. trichocarpa genome were characterised by phylogenetic analysis and their transcript accumulation patterns across a range of tissues and organs were assessed using whole genome poplar microarrays. Results of this analysis indicated that expansion and diversification of the R2R3-MYB family may have contributed to phenotypic innovation in the Populus lineage. Second, drought-responsive transcriptome adjustments of two hybrid poplar clones, DN34 (P. deltoides X P. nigra) and NM6 (P. nigra X P. maxiomowiczii) were assessed for time-of-day and genotype dependent patterns. For each genotype, each of four time points was characterised by discrete sets of drought-responsive genes. Furthermore, while a number of genes were identified that were responsive to drought in both genotypes, a much larger number of genotype-dependent, drought-responsive transcriptome changes were detected. Finally, the drought-responsive transcriptome adjustments A. thaliana plants were assessed for time-of-day dependent accumulation patterns. Results of this analysis indicate that time-of-day-dependent differences in the drought response were manifest as changes of different magnitudes for a conserved set of genes across the four time points measured. These results emphasise the complex interplay of a plant’s genome, developmental stage, and environment in shaping the observed transcriptome.

The relationship between an organism’s genome, developmental stage, and environment is complex. The aim of the research presented herein was to provide experimental evidence to contribute to the annotation of the P. trichocarpa genome and to test two major hypotheses addressing the interaction between drought and time of day in A. thaliana and in two hybrid Populus clones. In order to generate data to address these aims, three separate experiments were undertaken. First, all members of the R2R3-MYB family of transcription factors in the P. trichocarpa genome were characterised by phylogenetic analysis and their transcript accumulation patterns across a range of tissues and organs were assessed using whole genome poplar microarrays. Results of this analysis indicated that expansion and diversification of the R2R3-MYB family may have contributed to phenotypic innovation in the Populus lineage. Second, drought-responsive transcriptome adjustments of two hybrid poplar clones, DN34 (P. deltoides X P. nigra) and NM6 (P. nigra X P. maxiomowiczii) were assessed for time-of-day and genotype dependent patterns. For each genotype, each of four time points was characterised by discrete sets of drought-responsive genes. Furthermore, while a number of genes were identified that were responsive to drought in both genotypes, a much larger number of genotype-dependent, drought-responsive transcriptome changes were detected. Finally, the drought-responsive transcriptome adjustments A. thaliana plants were assessed for time-of-day dependent accumulation patterns. Results of this analysis indicate that time-of-day-dependent differences in the drought response were manifest as changes of different magnitudes for a conserved set of genes across the four time points measured. These results emphasise the complex interplay of a plant’s genome, developmental stage, and environment in shaping the observed transcriptome.

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