Regulatory mechanisms and evolutionary insights of phytoalexin biosynthesis in rice

Rice produces a diverse array of phytoalexins, including diterpenoid compounds (momilactones and phytocassanes) and the flavonoid sakuranetin, which serve as crucial defense metabolites against environmental stresses such as pathogen attack. This review summarizes the regulatory mechanisms and evolutionary insights of rice phytoalexin biosynthesis. Jasmonoyl-l-isoleucine (JA-Ile) is one of the signal molecules inducing phytoalexin production. OsCOI2 functions as the primary JA-Ile receptor for phytoalexin production. Multiple transcription factors, including DPF (Diterpenoid phytoalexin factor)/bHLH25 (basic helix-loop-helix 25), OsTGAP1 (Oryza sativa TGA factor for phytoalexin production 1), and various WRKY transcription factors, coordinately regulate the expression of biosynthetic genes. Remarkably, genes encoding diterpenoid phytoalexin biosynthetic enzymes are organized into biosynthetic gene clusters in the rice genome. Comparative genomic analyses reveal dynamic evolutionary processes involving gene duplications, cluster rearrangements, and occasional losses across Oryza species. These findings provide fundamental insights into the evolution of plant chemical defense and offer potential strategies for developing stress-tolerant crops by targeting the manipulation of phytoalexin biosynthetic pathways and their regulatory networks.