Abstract
Drought stress during the grain-filling stage severely limits sunflower (Helianthus annuus L.) productivity. Here, physiological, transcriptomic, and widely targeted metabolomic analyses were conducted in the drought-tolerant inbred line TDR1 and the drought-sensitive line ZDA279. TDR1 exhibited stronger osmotic adjustment and antioxidant responses under drought stress. Integrated multi-omics analysis revealed genotype-dependent changes in sucrose metabolism, amino acid metabolism, and phenylpropanoid biosynthesis. Ha4CL2, a gene associated with phenylpropanoid metabolism, was strongly induced by drought in TDR1. Silencing Ha4CL2 reduced lignin accumulation, impaired antioxidant-related responses, and increased drought sensitivity in TDR1. Yeast one-hybrid assays showed that HaMYB62 binds to the Ha4CL2 promoter, while transient dual-luciferase assays demonstrated that HaMYB62 represses Ha4CL2 promoter activity in plant cells. Moreover, HaMYB62 silencing compromised drought tolerance and altered antioxidant- and lignin-related traits. These findings identify Ha4CL2 as a contributor to drought adaptation and suggest that HaMYB62 and Ha4CL2 function within a broader regulatory network associated with phenylpropanoid-mediated drought responses in sunflower.