Rhizobia were isolated from the root nodules of Clitoria ternatea in Thailand. The phylogeny of the isolates was investigated using 16S rDNA and the internal transcribed spacer (ITS) region from 16S to 23S rDNA. The phylogenetic tree of the 16S rDNA showed that ten of the eleven isolates belonged to Bradyrhizobium elkanii, and one belonged to Bradyrhizobium japonicum. The topology of the ITS tree was similar to that of 16S rDNA. The acetylene reduction activity was higher for the nodules inoculated with the isolated B. elkanii strains than for those inoculated with B. japonicum strains. When C. ternatea plants were inoculated with various Bradyrhizobium USDA strains isolated from Glycine max, C. ternatea formed many effective nodules with B. elkanii, especially USDA61. However, acetylene reduction activity per plant and the growth were higher in C. ternatea inoculated with our isolates. From these data we propose that effective rhizobia inoculant were identified for C. ternatea cultivation.

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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.

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