Comprehensive analysis of the mechanisms underlying enhanced growth and root N acquisition in rice by the endophytic diazotroph, Burkholderia vietnamiensis RS1

Rina Shinjo, Aiko Tanaka, Daisuke Sugiura, Takamasa Suzuki, Kazuma Uesaka, Yumiko Takebayashi, Mikiko Kojima, Hitoshi Sakakibara, Daigo Takemoto, Motohiko Kondo

Aims The aim of this study was to provide a comprehensive understanding of the mechanisms underlying response of rice (Oryza sativa L.) to the endophytic N-2-fixing bacterium Burkholderia vietnamiensis strain RS1 in growth and nitrogen (N) accumulation using transcriptome and hormonome analyses. Methods The effects of B. vietnamiensis RS1 on rice growth and root architecture were examined in pot and field conditions. To identify candidate plant genes that affect the growth of plants inoculated with B. vietnamiensis RS1, transcriptome analysis was conducted. We also examined the hormonal changes by hormonome analysis in relation to the morphological changes in roots. The contribution of N-2 fixation by B. vietnamiensis RS1 was estimated by the acetylene reduction activity (ARA). Results The inoculation of B. vietnamiensis RS1 resulted in increased shoot and root growth of rice plants accompanied by an increased root N absorption rate, especially under high N conditions. The contribution from N-2 fixation was minor because no effect of B. vietnamiensis RS1 on ARA was detected. Transcriptome analysis revealed an increase in the expression of genes related to the transportation and assimilation of N compounds, supporting the enhanced N absorption by roots. The expression of indole-3-acetic acid (IAA) signaling genes and concentrations of IAA increased, which may be related to the increased root development. Conclusions B. vietnamiensis RS1 enhanced rice growth by promoting N accumulation through enhanced root morphological development and N absorption ability; this outcome was probably related to the increased activities of N transportation and assimilation in the presence of a rich N supply.