Effects of seasonal temperature changes on DkMyb4 expression involved in proanthocyanidin regulation in two genotypes of persimmon (Diospyros kaki Thunb.) fruit

Abstract

Persimmon fruits accumulate a large amount of proanthocyanidin (PA). Fruits of the mutant non-astringent (NA) type lose their ability to accumulate PA at an early stage of fruit development, whereas fruits of the normal astringent (A) type sustain PA accumulation until ripening. This allelotype is determined by the genotype of a single ASTRINGENCY (AST) locus. It is possible that the reduction in PA accumulation in NA-type fruits is due to phenological down-regulation of DkMyb4 (a PA regulator) and the resultant down-regulation of structural genes in the PA pathway. In this study, attempts were made to identify the regulatory mechanisms of phenological PA accumulation in A- and NA-type fruits, focusing particularly on the effects of ambient temperature. Continuous cool temperature conditions caused sustained expression of DkMyb4 in NA-type fruits, as well as in A-type fruits, resulting in increased expression of PA pathway genes and PA accumulation. However, the expression of some A/NA phenotypic marker genes was not significantly affected by the cool temperature conditions. In addition, PA composition in NA-type fruits exposed to cool temperatures differed from that in A-type fruits. These results indicate that a cool ambient temperature may have induced DkMyb4 expression and resultant PA accumulation, but did not directly affect the expression of the AST gene.

Seasonal Abscisic Acid Signal and a Basic Leucine Zipper Transcription Factor, DkbZIP5, Regulate Proanthocyanidin Biosynthesis in Persimmon Fruit

“…ABA concentration in persimmon fruit gradually decreases after anthesis until the middle fruit development stage. Similar tendencies are shown in A-and NA-type cultivars (Akagi et al, 2011;Supplemental Fig. S1).…”

“…2 and 3). Previous results demonstrate a temperature-dependent change that coincides with the endogenous ABA concentration and PA accumulation in NA-type fruit (Akagi et al, 2011). This explains why exogenous ABA and ABA inhibitors are effective only during specific periods, because the endogenous ABA concentrations are high only during early fruit development and are considerably down-regulated in the middle developmental stage (Kojima et al, 1999;Akagi et al, 2011;Supplemental Fig.…”

“…Previous reports on the phenological regulation of flavonoid biosynthesis in persimmon fruit and other tree crops, such as grapevine, would support this possibility. Artificial cool temperatures have an apparent effect on anthocyanin regulation in grape skin (Yamane et al, 2006) and on PA regulation in persimmon fruit flesh (Akagi et al, 2011) during specific developmental stages. Exogenous ABA treatment applied just before and after véraison promotes anthocyanin biosynthesis in grape skin through the up-regulation of VvMYBA1 expression (Ban et al, 2003;Jeong et al, 2004).…”

“…It has been suggested that NA-type fruitspecific down-regulation of DkMyb4, which is a Myb TF regulating PA and shikimate pathway genes, may reduce the expression of these genes, with a corresponding reduction in PA content in NA-type fruits (Akagi et al, 2009b). In addition, low temperatures affect the phenological expression of DkMyb4 and the resultant PA accumulation in NA-type cultivars, particularly in the early developmental stage, accompanied by a significant increase in ABA concentration, although this was not observed in the A-type cultivar (Akagi et al, 2011). These results suggest that further characterization of the phenological response of PA biosynthesis in persimmon would provide a good understanding of the signaling pathways regulating PA accumulation in response to seasonal and environmental factors.…”

Identification and characterization of MYB‐bHLH‐WD40 regulatory complexes controlling proanthocyanidin biosynthesis in strawberry (Fragaria × ananassa) fruits

“…They may act as antioxidants or as signalling molecules and were shown to be able to modulate some cellular functions (Nijveldt et al, 2001;Battino et al, 2009). Flavonoids such as PAs are also known to impact fruit flavour and astringency (Akagi et al, 2011).…”