Format: ORAL

Ranran Zhu1, Suhua Shi1*, Shaohua Xu1*

1 Sun Yat-sen University, Guangzhou, China *Corresponding author: Email: lssssh@mail.sysu.edu.cn & xushh27@mail.sysu.edu.cn

Whole-genome duplications (WGDs) are prevalent and provide extensive material in plant evolution process. The extensive gene loss and biased retention of duplicated genes after WGDs were proposed responsible for the environmental adaptation and species diversification, but the mechanisms are still rarely uncovered. In mangroves that inhabited intertidal environments independently from inland ancestors, we found the clades experienced WGD events had higher species diversity. We choose Avicennia genus, a typical mangrove clade with specified phenotypes and a high species diversity, to explore the possible molecular mechanisms of WGD in promoting species divergence. We first assembled seven high-quality mangrove genomes of the Avicennia genus using PacBio Single-Molecule Real-Time sequencing. Then, we identified two recent WGD events in Avicennia. The more recent one is Avicennia-specific, coinciding with the genuss origin approximately 46 million years ago. The WGD retained gene duplications are involved in high salt tolerance and nutrient absorption, contributing to the genus adaptation to intertidal environments. We test the role of reciprocal gene loss (RGL) in the rapid species divergence of the Avicennia genus. Combined with gene collinearity and phylogenetic analyses, we accurately identified RGL events among these species. Interestingly, a few RGLs between sister species are closely related to reproduction process, such as pollen tube invasion of the stigma. Further functional studies suggested that RGLs may cause reproduction isolation between sister species. In summary, our study uncovered the role of WGD in environmental adaptation and provided evidence that RGL after WGDs may be a potential speciation mechanism in mangrove plants.