Anthocyanin accumulation enhances drought tolerance in purple-leaf Brassica napus: Transcriptomic, metabolomic, and physiological evidence

Anthocyanins are flavonoid compounds that provide plants with various advantages, including resistance to abiotic stress, pollinator attraction, and antioxidant properties. The present study aimed to investigate the impact of anthocyanin accumulation on drought tolerance in two genotypes of Brassica napus; purple-leaf (PL) and green-leaf (GL). Transcriptomic, metabolomic, and physiological analyses were conducted under drought conditions induced by polyethylene glycol (PEG-6000) for 4 and 8 days, with an additional evaluation after 4 days of re-watering. After drought stress, the PL genotype showed higher anthocyanin content, relative water content, and total soluble sugar compared to the GL genotype. Furthermore, the PL genotype exhibited reduced levels of reactive oxygen species, higher antioxidant enzyme activities, and less damage to the chloroplast ultrastructure than the GL genotype. These results indicate that the PL genotype shows significant advantages over GL, demonstrating improved water holding capability and stress tolerance. Moreover, under mild drought and rewatering conditions, the PL genotype of B. napus exhibited significant upregulation of structural genes expression associated with the biosynthesis of flavonoids. These correlate with increased anthocyanin content, particularly cyanidin glycosides and flavanols. The PL genotype showed greater gene expression related to flavonoid biosynthesis, particularly anthocyanin production, compared to GL. Alongside, PL accumulated higher levels of anthocyanin-related metabolites. These results suggest that the enhanced flavonoid production contributes to greater drought resistance in PL. Additionally, by identifying important genes and metabolites related to anthocyanin accumulation and drought response, this integrated study provides insights into the intricate regulatory network that underlies these processes. These findings emphasize the potential of PL as a valuable genetic resource for developing drought-resistant rapeseed cultivars.