Role of a Newly Cloned Alternative Oxidase Gene (BjAOX1a) in Turnip Mosaic Virus (TuMV) Resistance in Mustard

A new alternative oxidase (AOX) gene, designated as BjAOX1a, of mustard (Brassica juncea) was cloned by reverse transcription-polymerase chain reaction (RT-PCR). The full-length cDNA of BjAOX1a was 1,346 bp in size and containing an open reading frame (ORF) of 1,083 bp in size. The predicted amino acid sequence exhibited 82.17% homology to the alternative oxidase of Arabidopsis thaliana. Analysis of functional regions revealed that the BjAOX1a protein contained several metal-binding regions, alpha-helical regions, and cysteine residues, similar to other AOX1 proteins. Pretreatment of mustard plants with salicylhydroxamic acid (SHAM), an inhibitor of AOX protein, inhibited AOX activity and promoted systemic movement of the coat protein of Turnip mosaic virus (TuMV), whereas pretreatment of plants with antimycin A (AA), a cytochrome pathway inhibitor, inhibited the systemic movement of the coat protein of TuMV. Furthermore, H2O2 and O2- contents were enhanced following SHAM pretreatment. Thus, AOX1 might alleviate reactive oxygen species (ROS) and enhance resistance of mustard plants to TuMV, and could serve as a critical component in TuMV resistance.