Gene expression and metabolite profiling of developing highbush blueberry (Vaccinium corymbosum L.) fruit indicates transcriptional regulation of flavonoid metabolism and activation of abscisic acid metabolism

摘要

Highbush blueberry (Vaccinium corymbosum L.) fruits contain substantial quantities of flavonoids, which are implicated in a wide range of health benefits. Although the flavonoid constituents of ripe blueberries are known, the molecular genetics underlying their biosynthesis, localization, and changes that occur during development have not been investigated. Two EST libraries from ripening blueberry fruit were constructed as a resource for gene identification and qRT-PCR primer design. Gene expression profiling by qRT-PCR showed that flavonoid biosynthetic transcript abundance followed a tightly regulated biphasic pattern, and transcript profiles were consistent with the abundance of the three major classes of flavonoids. Proanthocyanidins (PAs) and corresponding biosynthetic transcripts encoding anthocyanidin reductase (ANR) and leucoanthocyanidin reductase (LAR) were most concentrated in young fruit, and localized predominantly to the inner fruit tissue containing the seeds and placentae. Mean PA polymer length was 7 to 8.5 subunits, linked predominately via B-type linkages, and was relatively constant throughout development. Flavonol accumulation and localization patterns were similar to that of the PAs, and the B-ring hydroxylation pattern of both was correlated with flavonoid-3\u2032-hydroxylase transcript abundance. By contrast, anthocyanins accumulated late in maturation, which coincided with a peak in flavonoid-3-O-glycosyltransferase and flavonoid-3\u20325\u2032- hydroxylase transcripts. Transcripts of VcMYBPA1, which likely encodes an R2R3-MYB transcriptional regulator of PA synthesis, were prominent in both phases of development. Furthermore, the initiation of ripening was accompanied by a substantial rise in abscisic acid, a growth regulator that may be an important component of the ripening process and contribute to the regulation of blueberry flavonoid biosynthesis.