Soil salinity is a major threat to agriculture, significantly impacting crop yields in quality and quantity. This adversely affects socio-economic factors as well. Specifically in soybean plants, salt stress hinders growth and yield through osmotic imbalance, mineral deficiencies, and toxicity of specific ions. This leads to oxidative stress caused by producing reactive oxygen species (ROS). Our goal with this study was to uncover soybeans' molecular responses and adaptive strategies to salt stress, focusing on miRNA-mediated post-transcriptional regulation. We conducted experiments on two distinct Indian soybean cultivars: the salt-tolerant MAUS47 (Parbani Sona) and the salt-sensitive Gujosoya-2. These cultivars were exposed to short-term NaCl stress (100 mM) at the trifoliate stage. The two cultivars displayed distinct methods of scavenging reactive oxygen species and accumulating ions. The salt-sensitive variety had a higher intake of Na+ at the expense of essential K+, P+, and Mg2+ ions, which may have decreased yield and delayed growth. During salt stress, small RNA sequencing identified 450 miRNAs from various families, with miR159, miR3522, miR166, miR396, and others showing significant differential expression. Notably, miR159a-3p was identified as the top-responsive miRNA to salinity stress.
Further investigation revealed that miRNA159a-3p targets genes involved in hydrolase and carbohydrate-binding processes, specifically glutathione-S-transferase (GST), a crucial factor in salt tolerance. Validation through PCR confirmed the successful transformation of plants. Through this extensive investigation, we gain insight into the complex molecular processes that underlie soybean's reaction to high salinity levels. Specifically, the crucial involvement of miRNA159a-3p is highlighted, demonstrating its potential impact on promoting saline tolerance.