| Abstract |
Anthocyanin accumulation in grape berry skin is a crucial determinant of red/black grape berry quality. Recently, viticulture has been hampered by the issue of global warming, which has led to loss of anthocyanin accumulation in berry skin. The objectives of this study were to investigate the effect of allantoin on anthocyanin accumulation in berry skins of field-grown grapevines and to elucidate the molecular mechanism of the allantoin-induced anthocyanin accumulation in the berry skins. Allantoin enhanced anthocyanin accumulation in grape cultured cells and berry skins from field-grown grapevines at the early stage of ripening. MybA1 and UFGT, which encode the key transcription factor and enzyme in anthocyanin biosynthesis, were upregulated in allantoin-treated berry skins. Allantoin seems to increase the contents of delphinidin-based anthocyanin 3-glucosides in berry skins through the upregulation of F3'5'H gene that drives the synthesis of delphinidin-based anthocyanin 3-glucosides, compared with control berry skins. Allantoin increased soluble sugar contents in berries 10 days after treatment and upregulated abscisic acid (ABA)-responsible HT6 gene that encodes a key hexose transporter in sugar accumulation during ripening, in berry skins. These results suggested that physiological changes in allantoin-treated grape berries occurred in an ABA-dependent manner. Allantoin produced bioactive ABA through the β-glucosidase-catalyzed hydrolysis of glucose-conjugated ABA but not through the ABA biosynthesis by NCED, a key enzyme in ABA biosynthesis, in berry skins. Allantoin application in viticulture under global warming conditions is expected to contribute to mitigating loss of red/black berry skin color.
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