Dirigent (DIR) Proteins: Molecular Switching for Metabolism of Lignan to Making Climate Smart Plants

Dirigent (DIR) proteins are emerging as key molecular switches that integrate lignan metabolism with plant resistance in a changing climate. Initially identified in Forsythia intermedia as regulators of the stereoselective coupling of monolignols into (+)-pinoresinol, DIR proteins have since been discovered throughout terrestrial plants, exhibiting various subfamilies with distinct evolutionary pathways and functional specializations. Beyond their canonical role in lignan biosynthesis, DIRs facilitate lignin assembly, enhance cell wall fortification, and regulate reactive oxygen species (ROS) homeostasis, facilitating plants' dynamic adjustments to environmental challenges. Recent advancements reveal that DIR proteins function at the interplay of cellular metabolism and signaling processes, integrating phytohormonal pathways including abscisic acid, methyl-jasmonates, and cytokinins to synchronize responses to drought, salinity, high temperatures, heavy metal stress, and invasive pathogens. Monocot-specific Dirigent-Jacalin fusion proteins show evolutionary uniqueness by integrating pathogen identification with stereoselective phenolic metabolism, thus providing broad-spectrum resistance. Despite these advancements, significant questions remain concerning subfamily-specific studies, structural determinants of stereoselectivity, and the spatial-temporal control of DIR activity. Moreover, how DIR-mediated pathways balance out growth-defense trade-offs remains unknown. DIR proteins serve as regulators of diverse plant adaptation responses, and exploiting their functional diversity offers intriguing possibilities for developing climate-resilient, stress-tolerant, and highly productive crops for sustainable agriculture.