Growth under mild drought: transcriptomics comparison of perennial ryegrass genotypes with differential tolerance to water deficit

Mild summer droughts rarely threaten perennial ryegrass survival, but sensitive cultivars may halt growth early, reducing yields. This study examined the transcriptomic responses to mild drought (5 days without watering) and rewatering in two genotypes with contrasting leaf growth behaviors. The sensitive genotype showed a substantially higher number of differentially expressed genes (DEGs) than the tolerant one, including upregulated stress-related transcription factors (bZIP, DREB, MYB, and WRKY) and downregulated cell growth genes, consistent with its early growth arrest and autophagy activation. The tolerant genotype displayed delayed stress responses and upregulated genes for root development and water retention (TSO1 and WSD1), enabling continued growth through physiological adaptation. Both genotypes activated recovery pathways upon rewatering, particularly fatty acid and nucleotide synthesis, but the sensitive genotype exhibited abrupt shutdown of drought responses, limiting recovery. These findings reveal genotype-specific molecular strategies and candidate genes for breeding drought-resilient perennial ryegrass.