The genome of Lespedeza potaninii reveals biased subgenome evolution and drought adaptation.

Lespedeza potaninii, a xerophytic subshrub belonging to the legume family, is native to the Tengger Desert and is highly adapted to drought. It has important ecological value due to its drought adaptability, but the underlying molecular mechanisms remain largely unknown. Here, we report a 1.24 Gb chromosome-scale assembly of the L. potaninii genome (contig N50 = 15.75 Mb). Our results indicate that L. potaninii underwent an allopolyploid event with 2 subgenomes, A and B, presenting asymmetric evolution and B subgenome dominance. We estimate that the 2 diploid progenitors of L. potaninii diverged around 3.6 million years ago (MYA) and merged around 1.0 MYA. We revealed that the expansion of hub genes associated with drought responses, such as the binding partner 1 of accelerated cell death 11 (ACD11) (BPA1), facilitated environmental adaptations of L. potaninii to desert habitats. We found a novel function of the BPA1 family in abiotic stress tolerance in addition to the known role in regulating the plant immune response, which could improve drought tolerance by positively regulating reactive oxygen species homeostasis in plants. We revealed that bZIP transcription factors could bind to the BPA1 promoter and activate its transcription. Our work fills the genomic data gap in the Lespedeza genus and the tribe Desmodieae, which should provide theoretical support both in the study of drought tolerance and in the molecular breeding of legume crops.