ALBERT

Description: Aims In a large dam-regulated reservoir with regular hydrological pattern and strong flooding gradients across shore elevations, plants inhabiting in different shore elevations have to confront long-lasting flooding of differential intensities every year. Such persistent stress may lead to intraspecific differentiation of flooding tolerance in seeds. Echinochloa crusgalli var. zelayensis is a dominant annual plant in the shores of the Three Gorges Reservoir (TGR), which plays an important role in the shore vegetation. The objective of this study is to check whether intraspecific differentiation of seed flooding tolerance has occurred among E. crusgalli var. zelayensis populations in the TGR shores and whether such differentiation is associated with weak seed dispersal. Methods We collected seeds of E. crusgalli var. zelayensis from different populations in the TGR shores, and then placed them at four elevations in the shores flooded by reservoir impoundment. Parameters reflecting seed flooding tolerance including post-flooding percentage of intact seeds, seed germinability, seedling emergence rate were investigated for the seeds from different populations and undergoing flooding of different intensities. Floating time of seeds and speed of water level rise during impoundment were examined, and used to quantify dispersal potential of seeds in the shores of the TGR when flooded. Important Findings Both intact seed percentage and final seedling emergence rate after flooding significantly declined with increasing shore elevations where the seeds were collected, indicating that intraspecific differentiation in seed flooding tolerance has occurred among E. crusgalli var. zelayensis populations in the TGR shores after seven-year operation of the reservoir. The distance of seeds transported by rising water during reservoir impoundment was limited due to short floating time of the seeds and relatively low speed of water level rise in the reservoir. This would be favourable to the development of intraspecific differentiation in seed flooding tolerance.

Description: Genes duplicated by whole genome duplication (WGD) and small-scale duplication (SSD) have played important roles in adaptive evolution of all flowering plants. However, it still remains under-investigated how the distinct models of duplication events and their contending evolutionary patterns have shaped the genome and epigenomes of extant plant species. In this study, we investigated the contribution of the WGD- and SSD-derived duplicate genes to the genome evolution of one diploid and three closely related allotetraploid Panax species based on genome, methylome and proteome datasets. Our genome-wide comparative analyses revealed that while the ginseng species complex were recently diverged, they have evolved distinct overall patterns of nucleotide variation, cytosine methylation and protein-level expression. In particular, genetic and epigenetic asymmetries observed in the recent WGD-derived genes are largely consistent across the ginseng species complex. In addition, our results revealed that gene duplicates generated by ancient WGD and SSD mechanisms exhibited distinct evolutionary patterns. We found the ancient WGD-derived genes (i.e., ancient collinear gene) are genetically more conserved and hypo-methylated at the cytosine sites. In contrast, some of the SSD-derived genes (i.e., dispersal duplicated gene) showed hyper-methylation and high variance in nucleotide variation pattern. Functional enrichment analyses of the duplicated genes indicated that adaptation-related traits (i.e., photosynthesis) created during the distant ancient WGDs are further strengthened by both the more recent WGD and SSD. Together, our findings suggest that different types of duplicated genes may have played distinct but relaying evolutionary roles in the polyploidization and speciation processes in the ginseng species complex.