Genome-wide association studies of stomatal conductance reveal the function of BnaLEA4-5 in drought resistance in <i>Brassica napus</i>

Drought stress severely inhibits plant growth and yield, and plants have evolved various strategies to mitigate its effects. However, the genetic basis of photosynthetic traits and their responses during drought stress in Brassica napus (B. napus) remains poorly understood. In this study, we assessed photosynthetic traits in a natural population of 167 B. napus accessions under well-watered and mild drought stress conditions. Genome-wide association studies (GWAS) identified 106 quantitative trait locus (QTLs) associated with photosynthetic traits. Among these QTLs, a major QTL, qSC.A10.1, which associated with stomatal conductance under mild drought, was located. Within this region, a candidate gene, BnaA10.LEA4-5, which encodes a late embryogenesis abundant (LEA) protein, was identified. Functional verification revealed that BnaLEA4-5 promotes jasmonic acid (JA) biosynthesis, thereby reducing stomatal density and conductance and enhancing water use efficiency and drought resistance in B. napus. Further investigation showed that BnaLEA4-5 induces JA biosynthesis by upregulating AOS1 through the transcription factors EDT1 and RAP2.4, leading to MYC2-regulated reduction of stomatal density. These findings elucidate the genetic basis and molecular mechanism underlying photosynthetic adaptation to drought stress in B. napus and provide a genetic resource for genetic improvement of drought resistance in B. napus breeding.