Two haplotype-resolved genomes of highly heterozygous AAB allotriploid bananas provide insights into subgenome asymmetric evolution and banana wilt control
Bananas (Musa spp.) are one of the most important tropical fruits and staple food, which are of great significance to human societies. Plantain and Silk are two important banana subgroups, which are both triploid hybrids (AAB) between the wild diploid Musa acuminata and M. balbisiana. In this study, we reported the first haplotype-resolved genome assembly of Plantain and Silk bananas with genome size of approximately 1.4 Gb. We discovered widespread asymmetric evolution in the subgenomes of Plantain and Silk, which could be linked to frequent homologous exchanges (HEs) events. This is the first study to uncover the genetic makeup of triploid banana and verify that subgenome B harbors a rich source of resistance genes. Of the 88,078 and 94,988 annotated genes in Plantain and Silk, only 58.5% and 59.4% were present in all three subgenomes, with >50% genes containing differently expressed alleles in different haplotypes. We also found that Plantain is more resistant to banana Fusarium wilt, exhibiting a much faster defense response after pathogenic fungi infection. Many differentially expressed genes in abscisic acid, ethylene, jasmonic acid and salicylic acid pathways were identified in Plantain. Our analysis revealed that MpMYB36 promotes the biosynthesis of secondary cell wall and deposition of lignin by directly binding to the promoter of MpPAL and MpHCT, which allows Plantain to inhibit the penetration of early infection. Moreover, the insertion of the key carotenoid synthesis gene (CRTISO) may be the potential genetic basis for the richness of carotenoids in Plantain. Our study provides an unprecedented genomic basis for basic research and the development of elite germplasm in cultivated bananas.