Light modulates organ-specific gibberellin-abscisic acid crosstalk during drought response in Arabidopsis thaliana

Continuous blue light enhances drought tolerance in Arabidopsis by modulating ABA and GA pathways, whilst controlled GA catabolism, especially via GA2ox7/8, is important for stomatal regulation and drought adaptation. In response to drought, plants undergo physiological and developmental adjustments to reduce water loss and survive the stress, including reduced shoot growth, altered root architecture, and stomatal closure. These processes are regulated by phytohormones, including gibberellins (GAs), which mediate growth adjustments, and abscisic acid (ABA), which promotes stomatal closure. In addition, light signalling plays a crucial role in plant adaptation to drought. Here, we investigated how progressive water restriction affects hormone levels, gene expression, and leaf temperature in Arabidopsis thaliana shoots and roots under two contrasting light regimes: white light under short-day and continuous low-intensity blue light, with a focus on GA and ABA signalling pathways. The hormonal contribution to the drought response was investigated by analysis of ABA and GA mutants. Plants grown under continuous blue light experienced less-drought stress compared with white light as reflected in growth performance and differential gene expression. Drought increased ABA levels in leaves and roots, with stronger accumulation in roots under both light conditions. By contrast, GA production was decreased in leaves and increased in roots under drought in white light, but with little change in blue light. The change in GA status in leaves was associated with down-regulation of GA-biosynthetic 20-OXIDASE genes and up-regulation of GA-catabolic 2-OXIDASE genes (AtGA2ox6, AtGA2ox9). ABA- and GA-deficient mutants were unaffected by water restriction, whilst GA-overproducers lacking GA2ox genes or overexpressing AtGA20ox1 were hypersensitive to drought, with the C₂₀-GA2ox genes GA2ox7 and GA2ox8 proving particularly critical with compromised stomatal regulation.