Genomic insights into drought adaptation of the forage shrub <i>Caragana korshinskii</i> (Fabaceae) widely planted in drylands

The Korshinsk peashrub (Caragana korshinskii), known for its exceptional drought tolerance, is widely cultivated in arid and semi-arid regions for vegetation restoration and as a vital forage plant. To elucidate the genomic basis of its drought tolerance, we generated a chromosomal-scale genome sequence of C. korshinskii. Our synteny analysis disputes the previously hypothesized genus-specific whole-genome duplication event, as suggested by earlier transcriptome study of this species and its congeners. We identified that tandem duplications were critical for the expansion of gene families, such as early light-induced protein, heat shock protein 100, and Dehydrin, which are involved in cellular protection processes. These expansions are likely pivotal to the superior drought tolerance observed in C. korshinskii, as evidenced by the elevated gene expression of these genes under drought conditions. Furthermore, overexpression studies of seven tandemly duplicated DHN genes revealed a substantial enhancement in drought survival rates of seedlings, likely attributable to increased gene dosage effects. Conversely, gene silencing via virus-induced gene silencing demonstrated opposing effects. Additionally, we have established the CakorDB, a genomic resource database for C. korshinskii (https://bis.zju.edu.cn/cakordb/), accessible freely to the scientific community. Collectively, our study not only provides a valuable genomic resource for the Korshinsk peashrub but also highlights the genetic adaptations that enable C. korshinskii to thrive in desert environments, positioning its stress-responsive genes as a valuable genetic reservoir for breeding drought-resistant crops.