<scp>ABA</scp> insensitive 5 mediates abscisic acid regulation of plant photosynthesis by coordinating carbon and nitrogen assimilation

Photosynthesis is inextricably linked to plant biomass and productivity. Enhancing the capacity for photosynthetic carbon assimilation stands as a pivotal strategy to boost plant photosynthetic efficiency; however, progress remains limited. We identified the rog1 (repressors of glu1-1 1) mutant, which was screened as a genetic suppressor of glu1-1, an aberrant variant of Arabidopsis ferredoxin-dependent glutamate synthase (Fd-GOGAT) impaired in ammonium assimilation and photosynthesis. The ROG1 gene encodes the abscisic acid (ABA) biosynthesis enzyme ABA2. Exogenous ABA exerts inhibitory effects on carbon and nitrogen assimilation, thus diminishing photosynthetic rates, and these inhibitions are contingent upon ABA insensitive 5 (ABI5), a key component of the ABA signaling pathway. Further investigation revealed that ABI5 acts as a transcriptional repressor, directly interacting with the promoters of carbon assimilation genes RCA, RBCS2B, and RBCS3B, as well as the nitrogen assimilation gene GLU1, thereby impeding their transcriptional activity. Reducing ABI5 expression led to increased photosynthetic efficiency, growth, and productivity in both Arabidopsis and rice. This study highlights the critical role of ABI5 in plant photosynthesis by coordinating carbon and nitrogen assimilation, presenting a promising approach to enhance photosynthetic efficiency and agricultural productivity.