High Night Temperature Inhibits Anthocyanin Biosynthesis via Expression of MdMYB1 and MdMYBA in Hongro Apple Fruit Skins

Abstract

To estimate the effects of high night temperature (HNT) on skin coloration of Hongro apple fruit and to clarify the cause of reduced anthocyanin accumulation in the fruit skins under HNT on the gene expression level, expression patterns of structural genes and transcription factors in anthocyanin biosynthesis were analyzed. The a* and h0 scales of fruit skins under HNT changed more slowly than those of control, indicating that HNT inhibited red coloration in the skins. Anthocyanin accumulation in fruit skins was reduced by HNT, and the reduced accumulation was not recovered to the level of control at 2 weeks after the temperature treatment. Chlorophyll contents in fruit skins were not affected by different night temperatures. From quantitative real-time PCR analysis, all five structural genes, MdCHS, MdF3H, MdDFR, MdANS, and MdUFGT, were found to be up-regulated by low temperature and their expressions were correlated with anthocyanin accumulation in fruit skins. Transcription factors of anthocyanin biosynthesis, MdMYB1, MdMYBA, and MdbHLH3, were increased rapidly by low temperature. HNT decreased the expressions of these five structural genes and MdMYB1 and MdMYBA until 7 days after treatment. Among them, MdDFR and MdUFGT were significantly correlated with anthocyanin accumulation in fruit skins. In conclusion, anthocyanin biosynthesis in Hongro apple fruit skins was inhibited by HNT, concomitantly with the reduced expressions of anthocyanin biosynthetic genes and transcription factors MdMYB1 and MdMYBA. These results imply that MdMYB1 and MdMYBA are promising candidate genes for enhancing red coloration in apple fruit skins even under elevated night temperature.