AUTHOR=Arthikala Manoj-Kumar , Montiel Jesús , Sánchez-López Rosana , Nava Noreide , Cárdenas Luis , Quinto Carmen 

TITLE=Respiratory Burst Oxidase Homolog Gene A Is Crucial for Rhizobium Infection and Nodule Maturation and Function in Common Bean

JOURNAL=Frontiers in Plant Science

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2017.02003

DOI=10.3389/fpls.2017.02003

ISSN=1664-462X

ABSTRACT=<p>Reactive oxygen species (ROS) produced by respiratory burst oxidase homologs (RBOHs) regulate numerous plant cell processes, including the symbiosis between legumes and nitrogen-fixing bacteria. Rapid and transient ROS production was reported after <italic>Phaseolus vulgaris</italic> root hairs were treated with Nod factors, indicating the presence of a ROS-associated molecular signature in the symbiosis signaling pathway. <italic>Rboh</italic> is a multigene family containing nine members (<italic>RbohA–I</italic>) in <italic>P. vulgaris</italic>. RNA interference of <italic>RbohB</italic> suppresses ROS production and attenuates rhizobial infection thread (IT) progression in <italic>P. vulgaris</italic> root hairs. However, the roles of other <italic>Rboh</italic> members in symbiotic interactions are largely unknown. In this study, we characterized the role of the NADPH oxidase-encoding gene <italic>RbohA</italic> (Phvulv091020621) in the <italic>P. vulgaris</italic>–<italic>Rhizobium tropici</italic> symbiosis. The spatiotemporal activity of the <italic>RbohA</italic> promoter colocalized with growing ITs and was associated with vascular bundles in developing nodules. Subcellular localization studies indicated that RBOHA was localized in the plasma membrane of <italic>P. vulgaris</italic> root hairs. After rhizobial inoculation, PvRBOHA was mainly distributed in the infection pocket and, to a lesser extent, throughout the IT. In <italic>PvRbohA</italic> RNAi lines, the rhizobial infection events were significantly reduced and, in successful infections, IT progression was arrested within the root hair, but did not impede cortical cell division. <italic>PvRbohA</italic>-RNAi nodules failed to fix nitrogen, since the infected cells in the few nodules formed were empty. <italic>RbohA</italic>-dependent ROS production and upregulation of several antioxidant enzymes was attenuated in rhizobia-inoculated <italic>PvRbohA</italic>-RNAi roots. These combined results indicate that <italic>PvRbohA</italic> is crucial for effective <italic>Rhizobium</italic> infection and its release into the nodule cells. This oxidase is partially or indirectly required to promote nodule organogenesis, altering the expression of auxin- and cyclin-related genes and genes involved in cell growth and division.</p>