Construction of regulatory gene ttsI mutant in type III secretion system of Bradyrhizobium sp. MZ5 and its function analysis

Abstract:

[Objective] To explore the function of type Ⅲ secretion system of bradyrhizbial strains in peanut-rhizobia interaction. [Methods] We constructed the ttsI mutant of type Ⅲ secretion system in Bradyrhizobium sp. MZ5 by the way of homologous recombination and three parental conjugative transfer. The different expression of ttsI in MZ5 and MZ5ΔttsI were analyzed by real-time PCR by using the cDNA as templates after addition of Daidzein and Genistein. The vermiculite nodulation experiment was performed to comparative analysis of the nodulation ability of Bradyrhizobium sp. MZ5 and its ttsI mutant on Arachis hypogea (S523 and Y45).[Results] We found that daidzein and genistein had a significant inhibiting effect on the ttsI gene of the strain MZ5 (P<0.05). In the vermiculite nodulation experiment, we found that there was a significant reduction in the number of nodules and the shoot dry weight on peanut S523 and Y45 for MZ5ΔttsI mutant (P<0.05) comparing with the wild-type strain MZ5. The semi-thin nodule section showed that the MZ5ΔttsI mutant contained fewer cells in the nodules than the wild-type strain. [Conclusion] The type Ⅲ secretion system of Bradyrhizobium sp. MZ5 has a positive effect on peanut-rhizobia interaction.