The Endophytic Plant Growth Promoting Methylobacterium oryzae CBMB20 Modulates Plant Defense Responses while Integrating Naturally with the Seed-borne Endophytic Bacterial Community of Rice

다국어 초록 (Multilingual Abstract)

Inoculation with the endophytic plant growth promoting bacteria (PGPB) leads to plant responses concurrent to the integration of the bioinoculum to the native endophytic bacterial community of the host plant. The interaction of the bioinoculum on the community of the native endophytic bacteria of the host plant is also understudied but should be an essential factor when assessing effects of bioinoculants. The study evaluated the modulation of host defense responses in rice when it is inoculated by Methylobacterium oryzae CBMB20. The effect of inoculation on the diversity and community structure of the root and shoot bacterial endophytes in Oryza sativa L. spp. indica cv. IR29 was also investigated. The defense responses observed in IR29 measured in terms of ROS and PR protein production significantly increased, but was eventually modulated by Methylobacterium oryzae CBMB20. Using Terminal Restriction Fragment Length Polymorphism (T-RFLP) analysis, CBMB20 was shown to integrate with the native endophytic bacterial community of rice without causing significant changes in the bacterial diversity and community structure. The endophytic bacterial community of the rice seedling could be traced to the original seed community suggesting that they are seed-borne endophytes. The dominant bacterial communities in rice are mainly represented by bacterial genera associated to Microbacterium, Delftia, Pseudomonas, Xanthomonas and Stenotrophomonas, Herbaspirillum, Enterobacter and Sphingomonas. In addition, Curtobacterium, Enterobacter, Stenotro-phomonas and Xanthomonas were observed in both the root and shoot community. The results showed that Methylobacterium oryzae CBMB20 could modulate defense responses and non-antagonistically integrate with the native endophytic bacterial community of the rice host opening another area on the mechanism of plant growth promotion by the bioinoculum.