Evolutionary and functional analysis of the plant-specific NADPH oxidase gene family in Brassica rapa L.

NADPH oxidases (NOXs) have been known as respiratory burst oxidase homologues (RBOHs) in plants. To characterize the evolutionary relationships and functions of RBOHs in Brassica rapa, 134 RBOH homologues were identified from 13 plant species, including 14 members (namely BrRBOH01–14) from B. rapa. There presented 47 gene-pairs among 14 BrRBOHs and other RBOHs, consisting of five pairs within B. rapa, and 15 pairs between B. rapa and Arabidopsis thaliana. Together with phylogenetic analysis, the results suggested that whole-genome duplication might have played an important role in BrRBOH gene expansion, and these duplication events occurred after the divergence of the eudicot and the monocot lineages examined. Furthermore, gene expression of RBOHs in both A. thaliana and B. rapa were assayed via qRT–PCR. An RBOH gene, BrRBOH13 in B. rapa, was transformed into wild-type Arabidopsis plants. The transgenic lines with the overexpressed level of BrRBOH13 conferred to be more tolerant to heavy metal lead (0.05 mM) than wild-type plants. Overall, this integrated analysis at genome-wide level has provided some information on the evolutionary relationships among plant-specific NOXs and the coordinated diversification of gene structure and function in B. rapa.