Identification of NADPH oxidase family members associated with cold stress in strawberry

NADPH oxidase is encoded by a small gene family (Respiratory burst oxidase homologs, Rbohs) and plays an important role in regulating various biological processes. However, little information about this gene family is currently available for strawberry. In this study, a total of seven Rboh genes were identified from strawberry through genomewide analysis. Gene structure analysis showed the number of exons ranged from 10 to 23, implying that this variation occurred in FvRboh genes by the insertion and distribution of introns; the order and approximate size of exons were relatively conserved. FvRbohC was predicted to localize to the thylakoid membrane of the chloroplast, while other members were computed to localize to the plasma membrane, indicating different functions. Amino acid sequence alignment, conserved domain, and motif analysis showed that all identified FvRbohs had typical features of plant Rbohs. Phylogenetic analysis of Rbohs from strawberry, grape, Arabidopsis, and rice suggested that the FvRbohs could be divided into five subgroups and showed a closer relationship with those from grape and Arabidopsis than those from rice. The expression patterns of FvRboh genes in root, stem, leaf, flower, and fruit revealed robust tissue specificity. The expression levels of FvRbohA and FvRbohD were quickly induced by cold stress, followed by an increase in NADPH oxidase activity, leading to O-2(-) accumulation and triggering the antioxidant reaction by the transient increases in SOD activity. This suggested these two genes may be involved in cold stress and defense responses in strawberry.