KIX8 coordinates leaf development and light-induced stress responses in Medicago truncatula and Arabidopsis thaliana

Anthocyanins are flavonoid secondary metabolites primarily found in plant organs such as fruits and flowers, where they provide pigmentation and protect against light-induced stress. Although their levels are typically low in healthy green leaves, anthocyanins may accumulate in response to stress conditions. Plants have evolved intricate mechanisms to ensure proper leaf development while minimizing unnecessary anthocyanin accumulation in leaves under normal growth conditions. Unfortunately, these mechanisms remain largely unclear. Here we show that KIX8 plays a conserved role in preventing the production of anthocyanins in leaves while maintaining the proper expansion of leaves in Medicago truncatula and Arabidopsis thaliana. The mtkix8 mutant exhibited hypersensitivity to light intensity, with excessive anthocyanin accumulation on the abaxial leaf surface, particularly under high light conditions. This phenotype was associated with the upregulation of genes involved in anthocyanin biosynthesis. Further analysis revealed that MtKIX8 represses the expression of GRF-INTERACTING FACTOR 1 (MtGIF1), which further downregulates CONSTITUTIVELY PHOTOMORPHOGENIC 1 (MtCOP1), a key regulator of light signaling and anthocyanin accumulation. Our findings uncover the KIX8-GIF1-COP1 regulatory module that plays a critical role in preventing unnecessary anthocyanin accumulation, thereby optimizing plant growth and adaptation, and this provides new insights into the genetic mechanisms underlying KIX8-mediated coordination of leaf development and stress responses.