Transcriptome analysis of the differential effect of the NADPH oxidase gene RbohB in Phaseolus vulgaris roots following Rhizobium tropici and Rhizophagus irregularis inoculation

BackgroundReactive oxygen species (ROS) are generated by NADPH oxidases known as respiratory burst oxidase homologs (RBOHs) in plants. ROS regulate various cellular processes, including the mutualistic interactions between legumes and nitrogen-fixing bacteria or arbuscular mycorrhizal (AM) fungi.Rbohis a multigene family comprising nine members (RbohA–I) in common bean (Phaseolus vulgaris).The RNA interference-mediated silencing ofRbohB(PvRbohB-RNAi) in this species diminished its ROS production and greatly impaired nodulation. By contrast, thePvRbohB-RNAi transgenic roots showed early hyphal root colonization with enlarged fungal hypopodia; therefore, we proposed thatPvRbohBpositively regulates rhizobial infection (Rhizobium tropici) and inhibits AM colonization byRhizophagus irregularisinP. vulgaris.ResultsTo corroborate this hypothesis, an RNA-Seq transcriptomic analysis was performed to identify the differentially expressed genes in thePvRbohB-RNAi roots inoculated withRhizobium tropiciorRhizophagus irregularis. We found that, in the early stages, root nodule symbioses generated larger changes of the transcriptome than did AM symbioses inP. vulgaris. Genes related to ROS homeostasis and cell wall flexibility were markedly upregulated in the early stages of rhizobial colonization, but not during AM colonization. Compared with AM colonization, the rhizobia induced the expression of a greater number of genes encoding enzymes involved in the metabolism of auxins, cytokinins, and ethylene, which were typically repressed in thePvRbohB-RNAi roots.ConclusionsOur research provides substantial insights into the genetic interaction networks in the early stages of rhizobia and AM symbioses withP. vulgaris, as well as the differential roles thatRbohBplays in processes related to ROS scavenging, cell wall remodeling, and phytohormone homeostasis during nodulation and mycorrhization in this legume.