Characterization of the major latex protein gene family and functional analysis of GmMLP9 under salt stress in soybean

Abstract

Introduction The major latex proteins (MLPs) belong to the Bet v 1/PR-10 protein family, which is widely distributed among in higher plants and crucial for plant growth, hormone signaling, and abiotic stress responses. While MLP genes have been characterized in various plant species, the soybean MLP gene family and its contributions to salt tolerance remain poorly understood. Methods In this study, we integrated soybean genomic and transcriptomic data to comprehensively identify MLP family members using bioinformatics approaches. We systematically analyzed their physicochemical properties, phylogenetic relationships, gene structures, collinearity, promoter cis-regulatory elements, and expression profiles under NaCl and ABA treatments. Additionally, we validated the function of the candidate gene GmMLP9. Results A total of 41 MLP family genes were identified in the soybean genome, with protein lengths ranging from 125 to 319 amino acids. Phylogenetic analysis revealed that soybean MLP proteins clustered into three distinct subgroups: I, II, and IV. Collinearity analysis revealed 16 pairs of collinear genes within this family, which were predominantly distributed across various chromosomes, with higher densities observed on chromosomes 7 to 9, 15, and 17, all arising from segmental duplications. Selection pressure analysis indicated that the duplicated genes primarily experienced purifying selection throughout evolution. Promoter analysis identified numerous cis-regulatory elements associated with stress and hormone responses. Expression pattern analysis demonstrated that most MLP genes exhibited elevated transcript levels in roots. Under NaCl and ABA treatments, 19 candidate MLP genes showed varying degrees of upregulation or downregulation. Furthermore, overexpression of GmMLP9 significantly enhanced salt stress tolerance in both yeast and soybean plants. The soybean composite plants with GmMLP9-overexpressing hairy roots exhibited a lower Na+/K+ ratio and lower MDA content, but higher proline content. Discussion This study provides a theoretical foundation for further exploration of the MLP gene family’s role in soybean adaptation to salt stress and offers valuable insights for identifying candidate salt-tolerance genes and advancing molecular breeding efforts