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

Plant height is a key determinant of wheat plant architecture that determines lodging resistance thus grain yield. The GA-responsive (GAR) dwarfing gene Rht5 decreases plant height without comprise of wheat seedling vigor and is considered as a promising candidate gene for breeding wheat varieties in water-limited conditions. However, the mechanisms underlying Rht5 -meidated dwarfism is 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 was associated with the alteration of the homeostasis of endogenous growth-promoting phytohormones cytokine and gibberellins. Transcriptome analysis of identified TaGAD2 , encoding a functional glutamate decarboxylase localized at 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 mimic the phenotypes of dwarf Rht5 RILs 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 Rht5 -mediated plant height regulatory pathway and valuable gene resource to the genetic improvement of wheat plant architecture.