Genome-Wide Identification and Expression Analysis of the S-Locus-Specific Glycoprotein/EP1 Gene Family in Cotton (Gossypium hirsutum L.)

The S-locus-specific glycoprotein/EP1 gene family encodes a class of epidermis-specific secretory glycoproteins involved in plant responses to abiotic stress. However, their role in cotton (Gossypium hirsutum) drought response remains unclear. Here, we identified 12 GhEP1 genes from the G. hirsutum genome, clustered into three subfamilies. Structural predictions indicated that most GhEP1 proteins are hydrophilic and localised to the outer side of the plasma membrane or nucleus, with a few containing transmembrane domains. Collinearity analysis revealed that segmental and tandem duplications drove family expansion, with a high degree of collinearity conservation among dicotyledonous plants. Transcriptomic data showed generally low GhEP1 expression across tissues, but GhEP1-2, GhEP1-6, GhEP1-7 and GhEP1-8 responded significantly to NaCl, PEG-induced drought and cold stresses. qRT-PCR further confirmed that the expression of most GhEP1 genes was significantly up-regulated in roots under drought stress, while GhEP1-3 was induced in leaves, indicating tissue-specific regulatory divergence. This study systematically characterises the GhEP1 family and provides potential genetic resources for improving drought tolerance in cotton.