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

Abstract

It has previously been found that turnip mosaic virus (TuMV) greatly suppresses anthocyanin accumulation (AA) in Brassica rapa leaves, and that such leaves become infected whilst anthocyanin-enriched leaves on the same plants are rarely infected. To clarify whether AA is a defense against TuMV, in this study we examined tissue-level patterns of spontaneous AA in relation to the cellular localization of a TuMV strain that expresses a yellow fluorescent protein. We found that TuMV infection was significantly blocked by AA, suggesting that it functions as a chemical barrier against TuMV. We next analysed changes in expression of genes related to anthocyanin biosynthesis in TuMV-infected leaves of Arabidopsis. TuMV also suppressed AA that is induced by high light in Arabidopsis, and this this suppression was mainly due to inhibited expression of anthocyanin late-biosynthesis genes (LBGs). Most positive transcription factors of LBGs were also down-regulated, while the negative regulator SPL15 was highly up-regulated. Cucumber mosaic virus (CMV) also moderately suppressed AA in Arabidopsis, but in a different manner. Since it appeared that anthocyanin-enriched leaves of Arabidopsis were resistant to TuMV but not CMV, our results suggested that the anthocyanin-associated resistance that we observed was specific to TuMV.