A MYB-related transcription factor affects nodule formation in Lotus japonicus

The MYB family is one of the largest groups of transcription factors in plants. Our previous microarray data revealed that a MYB-related gene (Ljmybr) was induced upon nodule formation in Lotus japonicus. As shown using real-time PCR, the expression of the Ljmybr in L. japonicus was up-regulated after M. loti infection. To determine the role of Ljmybr in the nodulation process, we created transgenic hairy roots in L. japonicus and then performed Ljmybr overexpression (MYBOX) or RNAi-mediated suppression (MYBRNAi). The results of these experiments indicated that overexpressing Ljmybr accelerated L. japonicus nodulation and increased acetylene reduction activity (ARA) in the nodules. Suppressing Ljmybr (MYBRNAi) delayed nodulation and decreased ARA compared to control suppression (GUSRNAi). Seven days post infection, the expression levels of Nin, Enod40-1 and Enod40-2 were higher in MYBOX-treated nodules and lower in MYBRNAi-treated nodules. We propose that the Ljmybr transcription factor plays a role in regulating nitrogen fixation in L. japonicus.