Abstract: Light signaling coordinates plant development with metabolism, but the link between photoreceptors and chloroplast energy remains unclear. PKP1 produces pyruvate via plastid glycolysis, yet its integration with light signaling and whether blue light directly controls plastid primary carbon metabolism are unexplored. Here, we show that the soybean HY5 homologs SOYBEAN TGACG-MOTIF BINDING FACTOR 1 (GmSTF1) and GmSTF2 directly bind TGACGT motifs in the GmPKP1 promoter and activate its transcription, thereby establishing a direct regulatory link between the light signaling machinery and chloroplast pyruvate metabolism. Overexpression of GmPKP1 increased pyruvate levels and altered cellular energy status, leading to reduced plant height but increased pigment accumulation and enhanced photosynthetic performance. Field trials further revealed that GmPKP1 overexpression significantly increased pod number per plant, thereby enhancing individual plant yield, while concurrently reducing seed protein content and markedly increasing seed oil content. Genetic and metabolomic analyzes confirmed that GmSTF1/2 positively regulate plastid pyruvate metabolism and influence central carbon metabolic pathways, with GmPKP1 representing a key directly regulated node. Furthermore, the soybean blue-light photoreceptors GmCRY1a and GmCRY2a interact with GmSTF1/2 to enhance their transcriptional activity, whereas GmCOP1 suppresses this activation, thereby modulating GmPKP1 expression and pyruvate accumulation. Together, these findings define a CRYs-COP1-STF1/2-GmPKP1 module that directly couples blue light perception to chloroplast pyruvate metabolism. This represents a conceptual expansion beyond the canonical HY5-centered developmental paradigm, revealing that light signaling can directly regulate core plastidial carbon metabolism.

Key words: chloroplast glycolysis, elongated hypocotyl 5, pyruvate kinase plastids 1, soybean