The Interaction Between PGD2 and G6PD6 Is Involved in Aromatic Amino Acid Synthesis

The biosynthesis of AAAs in plants primarily relies on the shikimate pathway, with metabolic flux sustained by NADPH and E4P generated via the OPP pathway. However, how OPP enzymes coordinate to support AAA production remains unclear. Here, we investigated the direct interaction between two consecutive NADPH-producing enzymes, G6PD6 and PGD2, and its role in metabolic coupling. Using BiFC, Co-IP, pull-down assays, and domain mapping, we showed that G6PD6 and PGD2 form a cytosolic protein complex via the C-terminal domain of PGD2. Structural modeling identified potential interaction residues: PHE²⁹⁴, GLY²⁹⁷, and LEU²⁹⁸ in PGD2, and GLY³⁵¹, LYS⁴⁹⁹, and ALA⁵⁰⁰ in G6PD6. Overexpression of either enzyme partially rescued the dwarf phenotype of adh2 mutants caused by AAA deficiency. These findings indicate that the PGD2-G6PD6 complex coordinates OPP-derived reductive power and carbon flux to support downstream AAA biosynthesis. This study reveals a functional link between OPP enzyme interactions and AAA production, suggesting that metabolic flux can be regulated through direct enzyme-enzyme association. Future work will explore how this complex responds to metabolic demand and whether additional components contribute to coordinating flux between the OPP and shikimate pathways.