Format: ORAL

Xiao-Mei Xia

Institute of Botany, Chinese Academy of Sciences, Beijing, China

Evolutionary radiation is a widely recognized mode of species diversification, but its underlying mechanisms have not been unambiguously resolved for cosmopolitan plant genera. The factors that enable certain species-rich plant genera to adapt to diverse environments and achieve global distribution are still not fully understood. Rhododendron, as the largest genus of woody plants in the Northern Hemisphere, presents an exceptional system for investigating the genomic mechanisms driving evolutionary radiations and the capacity to adapt to a wide range of habitats. Here, we reconstructed the first completely resolved and dated phylogeny of Rhododendron, and found that most extant species originated by evolutionary radiations when the genus migrated southwards from circumboreal areas to tropical/subtropical mountains. We also found rapid increases of both net diversification rate and evolutionary rate of environmental factors in the Miocene, indicating that ecological factors have triggered the evolutionary radiations. Furthermore, we have accomplished high-quality, chromosomal-level genome assemblies of nine species and revealed diverse adaptive strategies employed by Rhododendron, particularly the adaptation to alpine and subalpine habitats by expansion/contraction of gene families involved in pathogen defense and oxidative phosphorylation, genomic convergent evolution, gene copy number variation, and a high percentage of private genes. The adaptation to high altitudes is further supported by our population genomic analysis of R. nivale, a species representing the highest altitudinal distribution within the genus and based on comprehensive range-wide sampling. Moreover, using metabolomic, transcriptomic, and genomic analyses, we have identified the genes involved in the biosynthesis of anthocyanins and carotenoids. This study provides a good example of integrating phylogenomic and ecological analyses in deciphering the mechanisms of plant evolutionary evolutions. It holds considerable significance in enhancing our understanding of plant adaptive evolution and offers valuable insights for improving flower colors in this important horticultural plant genus.