Genome-wide Analysis of Root Hair Preferred RBOH Genes Suggests that Three RBOH Genes are Associated with Auxin-mediated Root Hair Development in Rice

Plant homologs of mammalian NADPH oxidase, respiratory burst oxidase homologs (RBOH), mainly oxidize NADPH to NADP(+) and transfer electrons to water. The membrane residing RBOHs thus produce reactive oxygen species (ROS), which allows plants to withstand abiotic and biotic environmental stresses. To understand the spatial and temporal function of rice (Oryza sativa) RBOH genes, we performed expression analysis of nine RBOH genes using qRT-PCR and microarray data. The expression profiling data suggest that RBOH genes have diverse roles in various tissues and organs as well as responses to hormonal treatments. Among them, OsRBOH2, OsRBOH3, and OsRBOH5 are preferentially expressed in root hairs. Exogenous auxin upregulates the expression of OsRBOH1, OsRBOH2, OsRBOH3, OsRBOH4, and OsRBOH8 in root hairs, while the expression of OsRBOH7 and OsRBOH9 is downregulated. In roots, treatment with an RBOH inhibitor, diphenyleneiodonium (DPI), suppressed the accumulation of ROS in trichoblast cells which initiate root hairs, suggesting that RBOH-mediated ROS could play an important role in root hair initiation in the trichoblast cells of rice roots. Promoter analysis revealed that OsRBOH3 and OsRBOH5 contain many known cis-acting regulatory elements (CREs) associated with root hair development such as the root hair cis-acting element, RHE. OsRBOH2 and OsRBOH3, which are upregulated after treatment with indole-3-acetic acid (IAA) with significant expression in root hairs, might be key players in root hair elongation via an auxin-dependent pathway in rice.