Optimizing plant architecture is an efficient approach for breeders to adapt crops to changing environmental conditions and hence to potentially improve yields to meet the demands of a growing global population. Plant height and shoot branching play crucial roles in determining plant architecture, and they are mainly regulated by phytohormones, including brassinosteroids (BRs) and gibberellins (GAs). 

The researchers conducted phylogenetic analysis and amino acid sequencing. The results showed that DIB1 encodes a gibberellin 3β-hydroxylase (GA3ox) enzyme, catalyzing the final step of the biosynthetic pathway for bioactive GAs. 

They further found that endogenous concentrations of GA₄ and GA₁ were decreased in the dib1 mutant. The exogenous application of GA₃ rescued the mutant phenotypes, indicating that DIB1 was necessary for GA biosynthesis in M. truncatula. 

The results suggested that DIB1, a GA biosynthetic gene, might positively regulate the expression of MtBRC1, a key integrator of numerous signals, to control axillary bud outgrowth via influencing the biosynthesis of bioactive GAs in M. truncatula.  

"Our findings thus shed light on the control of axillary bud outgrowth by GAs in legumes. DIB1 could be a good candidate gene for breeders to optimize plant architecture for crop improvement," said Prof. CHEN Jianghua, principal investigator of the study. 

Gibberellins inhibits axillary bud outgrowth in Medicago truncatula (Image by ZHANG Xiaojia)