Battle for control of anthocyanin biosynthesis in two Brassicaceae species with turnip mosaic virus


 We previously noted that turnip mosaic virus (TuMV) greatly suppresses anthocyanin accumulation (AA) in Brassica rapa leaves that do become infected and that anthocyanin-enriched leaves in those plants are rarely infected with TuMV. To clarify whether AA is a defense against TuMV, we here examined the tissue-level patterns of spontaneous AA in relation to the cellular localization of a TuMV strain that expresses a yellow fluorescence protein. We found that TuMV infection was significantly blocked by AA, suggesting that AA functions as a chemical barrier against TuMV. Next, we analyzed changes in expression of anthocyanin biosynthesis-related genes in TuMV-infected leaves of Arabidopsis thaliana (Arabidopsis) to elucidate how TuMV controls anthocyanin biosynthesis. TuMV also suppressed AA that is induced by high light in Arabidopsis; this suppression of AA was mainly due to inhibited expression of the late anthocyanin biosynthesis genes (LBGs). Most positive transcription factors of LBGs were also downregulated, while the negative regulator SPL15 was highly upregulated. Cucumber mosaic virus (CMV) also moderately suppressed AA in Arabidopsis in a different manner. Because it seemed that anthocyanin-enriched leaves of Arabidopsis were resistant to TuMV but not CMV, it was suggested that the anthocyanin-associated resistance was specific to TuMV.