Format: ORAL

Jin-Ren Yu1,2,3, Ju Zhou1,2, Rindra M. Ranaivosona1,2,3, Romer N. Rabarijaona1,2,3, Zhi-Duan Chen1,2,4, Li-Min Lu1,2

1 Institute of Botany, Chinese Academy of Sciences, Beijing, China 2 China National Botanical Garden, Beijing, China 3 University of Chinese Academy of Sciences, Beijing, China 4 Sino-Africa Joint Research Center, Chinese Academy of Sciences, Wuhan, China

Cyphostemma, the second largest genus (ca. 200 species) of the grape family, mainly distributes in continental Africa and Madagascar. Species of the genus have colonized various habitats including tropical rainforests, savanna, and deserts. The genus exhibits extraordinary diversity in morphological innovations, of which the development of succulent stem is the most striking. Previous studies revealed a disparity in genome size, which has been suggested to be related to the innovation of succulence. However, it remains unclear how the genome size diversity in Cyphostemma is generated, and how it contributes to the adaptation to various habitats. We investigate this problem from both the genomic and ecological aspects. We assembled genomes of two representative species of Cyphostemma, C. dehongense from the Asian rainforest and C. currorii from the African desert. We find that genomes of Cyphostemma are mainly inflated by the insertion of long terminal repeat retrotransposons (LTR-RT), especially the explosive insertions of several families in the Ale lineage. According to the dynamics of LTR-RT, these families show a preference for inserting into introns since the Oligocene-Miocene Boundary, when Vitaceae began to diversify rapidly. The intron-preferring LTR-RT families have a higher death rate, and the genes with longer introns are under more relaxed selection, suggesting the co-evolution of LTR-RTs and their host genome. To further investigate the relationships between LTR-RT amplification and environmental conditions, we collected genomic repeat profiles, genome size, and habitat climatic factors for more than 100 taxa in Cyphostemma. Analyses based on a linear model reveal that genome expansion is generally associated with adaptation to aridity, but is limited by precipitation during the growing season. Moreover, we find that succulent species from arid regions of continental Africa and Madagascar exhibit different patterns of LTR-RT amplification, indicating different mechanisms for the origin of succulence.