Functional Characterization of GbERF13 Reveals Its Role in ABA-Responsive Fiber Development and Molecular Marker Development in Sea Island Cotton

Sea Island cotton (Gossypium barbadense L.) is a premium raw material for high-end textiles due to its excellent fiber quality. The AP2/ERF transcription factor family plays critical roles in plant growth and hormone signaling. Here, 161 GbERF family members were identified in Sea Island cotton and classified into nine subgroups, with GbERF13 belonging to Group V. Expression analysis revealed that GbERF13 was specifically and highly expressed in fibers, with transcript abundance peaking at 15–30 days post-anthesis (DPA), coinciding with the transition from fiber elongation to secondary wall thickening. Exogenous abscisic acid (ABA) treatment significantly induced GbERF13 expression and inhibited fiber elongation. Heterologous overexpression of GbERF13 in Arabidopsis increased trichome and root hair numbers while suppressing primary root growth, confirming its role in cell elongation and development. A nonsynonymous SNP (A/C) at the 117th base pair of the GbERF13 coding region (GbERF13-117SNP) was identified in 213 Sea Island cotton accessions. Association analysis showed the C allele was significantly and positively associated with fiber length, strength, and uniformity. An allele-specific PCR marker was further developed for molecular breeding. Collectively, GbERF13 acts as a key ABA-responsive transcription factor regulating fiber development, and its functional SNP marker provides a valuable tool for improving Sea Island cotton fiber quality.