Genomic insights into molecular adaptation to intertidal environments in the mangrove Aegiceras corniculatum.

Mangroves have colonised extreme intertidal environments characterised by high salinity, hypoxia and other abiotic stresses. Aegiceras corniculatum, a pioneer mangrove species that has evolved two specialised adaptive traits (salt secretion and crypto-vivipary) is an attractive ecological model to investigate molecular mechanisms underlying adaptation to intertidal environments. We assembled de novo a high-quality reference genome of A. corniculatum and performed comparative genomic and transcriptomic analyses to investigate molecular mechanisms underlying adaptation to intertidal environments. We provide evidence that A. corniculatum experienced a whole-genome duplication (WGD) event c. 35 Ma. We infer that maintenance of cellular environmental homeostasis is an important adaptive process in A. corniculatum. The 14-3-3 and H+ -ATPase protein-coding genes, essential for the salt homeostasis, were preferentially retained after the recent WGD event. Using comparative transcriptomics, we show that genes upregulated under high-salt conditions are involved in salt transport and ROS scavenging. We also found that all homologues of DELAY OF GERMINATION1 (DOG1) had lost their heme-binding ability in A. corniculatum, and that this may contribute to crypto-vivipary. Our study provides insight into the genomic correlates of phenotypic adaptation to intertidal environments. This could contribute not only within the genomics community, but also to the field of plant evolution.