Abstract
This study supports the idea that the evolution of type III secretion system (T3SS) is one of the factors that controls Vigna radiata–bradyrhizobia symbiosis. Based on phylogenetic tree data and gene arrangements, it seems that the T3SSs of the Thai bradyrhizobial strains SUTN9‐2, DOA1, and DOA9 and the Senegalese strain ORS3257 may share the same origin. Therefore, strains SUTN9‐2, DOA1, DOA9, and ORS3257 may have evolved their T3SSs independently from other bradyrhizobia, depending on biological and/or geological events. For functional analyses, the rhcJ genes of ORS3257, SUTN9‐2, DOA9, and USDA110 were disrupted. These mutations had cultivar‐specific effects on nodulation properties. The T3SSs of ORS3257 and DOA9 showed negative effects on V. radiata nodulation, while the T3SS of SUTN9‐2 showed no effect on V. radiata symbiosis. In the roots of V. radiata CN72, the expression levels of the PR1 gene after inoculation with ORS3257 and DOA9 were significantly higher than those after inoculation with ORS3257 ΩT3SS, DOA9 ΩT3SS, and SUTN9‐2. The T3Es from ORS3257 and DOA9 could trigger PR1 expression, which ultimately leads to abort nodulation. In contrast, the T3E from SUTN9‐2 reduced PR1 expression. It seems that the mutualistic relationship between SUTN9‐2 and V. radiata may have led to the selection of the most well‐adapted combination of T3SS and symbiotic bradyrhizobial genotype.
Highlights
Despite the massive number of number of bacteria in nature, only a few species can form symbiotic nodules with leguminous plants
To examine the evolutionary relationships of bradyrhizobial strains, the nucleotide sequences of the 16s rRNA gene from various refer‐ ence strains of Bradyrhizobium, Sinorhizobium, Mesorhizobium, and Rhodopseudomonas species were used to construct a phylogenetic tree
The nucleotide sequences were aligned using the ClustalW program, and the phylogenetic trees based on the 16S rRNA and T3SS gene sequences were constructed using the maximum‐likelihood method with PhyML (Guindon & Gascuel, 2003)
Summary
Despite the massive number of number of bacteria in nature, only a few species can form symbiotic nodules with leguminous plants. Bradyrhizobia can establish symbiotic re‐ lationships with several types of leguminous plants. Nod factors allow bradyrhizobia to enter the root hairs of leguminous. | 2 of 16 plants, other bacterial substances are required for productive infec‐ tion and nodule development (Mathis et al, 2005). Among these fac‐ tors are proteins secreted via the type III secretion systems (T3SSs; Okazaki, Kaneko, Sato, & Saeki, 2013; Tsukui et al, 2013). The genetic basis of how T3SSs are involved in the enhancement and suppression of nodulation in both partners in V. radiata bradyrhizobia symbiotic relationships has not been clearly elucidated. The current study is an important step toward understanding the functions of T3SSs in mutualistic relationships
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
