TaGAD2 is a potential downstream effector of Rht5 in controlling wheat plant height

Plant height is a key determinant of wheat plant architecture that affect lodging resistance and grain yield. The GA-responsive (GAR) dwarfing gene Rht5 was previously shown to decrease plant height without compromise of wheat seedling vigor and considered as a promising candidate gene for breeding wheat varieties in water-limited conditions. However, the mechanisms underlying Rht5-mediated dwarfism are unclear. In this study, we investigated the genetic effects of Rht5 on wheat growth and development using recombinant inbred lines (RILs) and found that Rht5 reduces plant height through inhibition of cell proliferation while it promotes cell elongation. The dual functions of Rht5 on cell growth during wheat stem elongation were associated with the alteration of the homeostasis of endogenous growth-promoting phytohormones cytokinins and gibberellins. Transcriptome analysis of Rht5 RILs and their parental lines identified TaGAD2 (glutamate decarboxylase), encoding a functional glutamate decarboxylase localized at the plasma membrane that catalyzes γ-aminobutyric acid (GABA) biosynthesis, as a potential downstream regulator of Rht5-mediated dwarfism. Functional assays demonstrated that overexpression of TaGAD2 could reduce plant height while TaGAD2 knockdown increased plant height and improved lodging resistance, indicating a negative role of TaGAD2 in controlling wheat plant height. We also conducted haplotype analysis of TaGAD2 in a natural wheat population and identified TaGAD2^H1 as a potential favorable allele for wheat dwarfing breeding without compromising grain number. Our study provides new insights into the molecular mechanism of the Rht5-mediated plant height regulatory pathway and valuable gene resource for the genetic improvement of wheat plant architecture.