GWAS and transcriptome analyses unravel ZmGRAS15 regulates drought tolerance and root elongation in maize

Drought is a major abiotic stress affecting maize development and growth. Unravelling the molecular mechanisms underlying maize drought tolerance and enhancing the drought tolerance of maize is of great importance. However, due to the complexity of the maize genome and the multiplicity of drought tolerance mechanisms, identifying the genetic effects of drought tolerance remains great challenging.

Using a mixed linear model (MLM) based on 362 maize inbred lines, we identified 40 associated loci and 150 candidate genes associated with survival rates. Concurrently, transcriptome analysis was conducted for five drought - tolerant and five drought - sensitive lines under Well-Watered (WW) and Water-Stressed (WS) conditions. Additionally, through co-expression network analysis (WGCNA), we identified five modules significantly associated with the leaf relative water content (RWC) under drought treatment. By integrating the results of GWAS, DEGs, and WGCNA, four candidate genes (Zm00001d006947, Zm00001d038753, Zm00001d003429 and Zm00001d003553) significantly associated with survival rate were successfully identified. Among them, ZmGRAS15 (Zm00001d003553), a GRAS transcription factor considered as a key hub gene, was selected for further functional validation. The overexpression of ZmGRAS15 in maize could significantly enhance drought tolerance through regulating primary root length at the seedling stage.

This study provides valuable information for understanding the genetic basis of drought tolerance and gene resources for maize drought tolerance breeding.