Exogenous abscisic acid enhances foxtail millet grain weight under drought stress: Insights from integrative transcriptomics and weighted gene co‐expression network analysis

Abstract BACKGROUND This study aimed to explore the underlying regulatory mechanism by which exogenous abscisic acid (ABA) application influences foxtail millet grain weight under drought stress at the heading–flowering stage. A two‐year field experiment was conducted with two irrigation treatments (well‐watered (CK) and drought stress (DS)) and four ABA concentrations (0, 10, 20, and 30 mg L −1 , designated as T1–T4). The grain filling rate and grain weight were measured, and transcriptome sequencing and weighted gene co‐expression network analysis (WGCNA) were performed at three stages to select candidate genes regulating grain weight. RESULTS The grain weight exhibited an S‐shaped growth pattern during the grain‐filling period. Compared with CK, drought stress significantly reduced the grain‐filling rate and grain weight, decreasing yield by 12.45% to 23.84%. Exogenous ABA application, especially the T3 treatment, significantly increased the grain‐filling rate, extended the grain‐filling duration, and enhanced grain weight, thereby mitigating drought‐induced yield loss. Transcriptome sequencing generated 290.19 Gb of clean data and 23,247 differentially expressed genes (DEGs) with the highest number of DEGs in the T3 versus T1 comparison at 30 days after flowering. Subsequently, WGCNA identified ten co‐expression modules, with the blue and magenta modules showing the strongest positive correlation with grain weight. Moreover, eight transcription factors (TFs) genes were identified as potential regulators of grain development under drought stress and ABA treatments. CONCLUSION Exogenous ABA application at 20 mg L −1 effectively increased the grain‐filling rate and grain weight and stabilized yield under drought stress. This improvement was associated with the activation of starch and sucrose metabolism and hormone signaling pathways, potentially coordinated by key TFs including the B3 , NAC , and WOX families. © 2026 Society of Chemical Industry.