Comparative physiological and transcriptomic analysis of two contrasting soybean genotypes reveals complex mechanisms involved in drought avoidance

To overcome drought stress in soybean (Glycine max), it is strategically vital to improve drought resistance. Yet, the underlying molecular mechanisms responsible for drought resistance remain poorly defined. Here, we present comparative physiological and transcriptome analyses in seedlings of two contrasting genotypes, drought-resistant (DR) L14 and drought-sensitive (DS) L21 in response to polyethylene glycol (PEG)-induced drought stress. Each genotype was subjected to 20% PEG along with control (0% PEG) in a greenhouse, and the leave samples were collected to determine the physiological traits and transcriptome profiling. With the accumulation of abscisic acid (ABA) under drought stress, the DR genotype exhibited higher water retention capability and slow-wilting phenotype compared to DS genotype. As nonsignificant changes in oxidative damages and antioxidant defenses, overcoming drought stress in DR genotype was facilitated by drought avoidance rather than drought tolerance. There were 1567 and 4029 differentially expressed genes (DEGs) identified in the DR and DS genotypes, respectively. The DEGs were mostly enriched in photosynthesis, carbohydrate metabolism, lipid metabolism, cell wall organization, and signaling pathways, which were less affected in DR genotype. However, most of the leucine-rich repeat receptor-like kinases (LRR-RLKs) were uniquely downregulated in DS genotype but uniquely upregulated in DR genotype by drought stress. By protein-protein interaction network analysis and whole genome resequencing, six LRR-RLKs were considered the potential candidate genes for drought avoidance. We suggested that these LRR-RLKs may play a critical role in promoting ABA-induced stomatal closure through enhancing ABA sensitivity, but this hypothesis needs further validation. Taken together, these findings could provide in-depth insights into the physiological and molecular mechanisms associated with drought avoidance and facilitate the breeding of drought-resistant soybean cultivars. The L14 had higher water retention capability and slow-wilting phenotype compared to L21 under drought stress.The differentially expressed genes (DEGs) associated with several metabolisms were more affected by drought stress in L21 rather than L14.Six leucine-rich repeat receptor-like kinases (LRR-RLKs) genes would be considered potential candidates for drought resistance but need further validation.