摘要：Abstract: Genome size and drought tolerance are two important traits that can influence life history strategies and reproductive success in plants. My current work uses a diverse set of disciplines, such as computational genomics, phylogenetic comparative biology, and physiological ecology, to gain insights into genome size variation in sunflowers (genus Helianthus) and evolution of drought tolerance in grasses (family Poaceae).
Using phylogenetic comparative methods, I demonstrated that different rates of genome size evolution are apparent across the sunflower phylogeny and identified significant negative associations of genome size with temperature seasonality and cell production rate. These results suggest that the evolution of larger genome size is more permissible in habitats with longer growing seasons, potentially because of negative correlations of nuclear genome size with whole-plant relative growth rates and a positive correlation with minimum generation times. Therefore, we hypothesize that genome size evolution in Helianthus diploid species is governed by natural selection on allowable rates of plant growth in different environments. I also demonstrated that the genomes harbor the same diverse gypsy and copia sublineages of LTR-RTs, but with gypsy sequences more abundant than copia across the phylogeny. Low but detectable transcriptional activity was observed for multiple gypsy and copia elements, but with a higher proportion of copia elements found to be active transcriptionally and with these copia elements expressed at higher levels. These observations are consistent with the notion that elements that are more abundant in the genome (i.e., gypsy) are more likely to be targeted for silencing by genomic surveillance mechanisms and those elements at lower abundances may be more likely to escape such targeting.
Drought is a major environmental stress that can affect plant growth and reproduction. Studies of wild plant species with natural drought tolerance will facilitate better understanding of the anatomical, physiological and molecular mechanisms through which plants cope with limited water availability associated with drought-like conditions. I examined physiological and transcriptional responses via RNA-seq of four grass species, two C3 and two C4 plants, at multiple time points during increased water stress and then during recovery following re-watering. Dry-down experiment showed plants experienced slight to dramatic physiological changes as drought stress became severe in all four species. Correspondingly, gene expression analysis indicated larger number of genes involved in gene regulation (particularly, genes coding for transcription factors), photosynthesis, and ABA-pathway were differentially expressed as plants experienced increasing drought stress in both C3 and C4 plants. Interestingly, we observed greater gene expression responses in less tolerant species, but for C3 plants only. Moreover, results indicated differential recovery of gene expression involved in photosynthesis between C3 and C4 plants. Collectively, these results revealed the temporal physiological and gene expression alterations during drought stress and recovery stage and provided a comprehensive list of candidate genes that are involved in regulatory mechanisms during drought stress for non-model plant species.
