Genome-wide identification of GmHVA22 gene family in soybean and functional analysis of GmHVA22-12 in salt stress

Plant HVA22 proteins constitute a distinct class of Abscisic acid (ABA)- and stress-induced proteins that play significant roles in plant adapt to environmental stress. However, the function of HVA22 genes under salt stress in soybean is largely unknown. In this study, 116 HVA22 members were identified in soybean, Arabidopsis, cotton, rice, maize, and potato, 29 of which came from soybean, designated as GmHVA22-1–29. Based on phylogenetic analysis and structural characterization of these genes, the HVA22 gene family was conserved in different plant species and could be divided into five principal groups (class I-V). The expansion of the GmHVA22 gene family was primarily driven by tandem and segmental duplications, with most duplicated pairs originating from a recent whole-genome duplication. Furthermore, qRT-PCR analysis showed that the expression of GmHVA22 genes was significantly altered under salt stress. RNA-seq analysis further revealed that GmHVA22-12 mediates salt tolerance by regulating the oxidation–reduction process. Consistent with the transcriptomic data, the gmhva22-12 mutation increased sensitivity to salt stress, as reflected in decreased activities of the antioxidant enzymatic catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD), while concurrently increasing the levels of H₂O₂ and malondialdehyde (MDA). In contrast, GmHVA22-12-overexpression improved salt tolerance by enhancing root growth and improving the activities of antioxidant enzymes (CAT, POD, and SOD) as well as MDA level relative to control plants. This study presents a comprehensive investigation of the GmHVA22 gene family in soybean, focusing on its genomic organization, evolutionary dynamics, expression profiles, and functional role in salt stress tolerance. This work not only elucidates the function of a specific stress-tolerant gene but also provides a framework for understanding the evolutionary and functional complexity of the entire HVA22 family in crops.