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

Takashi Akagi,Akihiko Sato,Ayako Katayama-Ikegami,Keizo Yonemori,Shozo Kobayashi,Atsushi Kono

doi:10.1104/pp.111.191205

Takashi Akagi, Akihiko Sato + Show 4 more

Open Access

https://doi.org/10.1104/pp.111.191205

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Abstract

Proanthocyanidins (PAs) are secondary metabolites that contribute to plant protection and crop quality. Persimmon (Diospyros kaki) has a unique characteristic of accumulating large amounts of PAs, particularly in its fruit. Normal astringent-type and mutant nonastringent-type fruits show different PA accumulation patterns depending on the seasonal expression patterns of DkMyb4, which is a Myb transcription factor (TF) regulating many PA pathway genes in persimmon. In this study, attempts were made to identify the factors involved in DkMyb4 expression and the resultant PA accumulation in persimmon fruit. Treatment with abscisic acid (ABA) and an ABA biosynthesis inhibitor resulted in differential changes in the expression patterns of DkMyb4 and PA biosynthesis in astringent-type and nonastringent-type fruits depending on the development stage. To obtain an ABA-signaling TF, we isolated a full-length basic leucine zipper (bZIP) TF, DkbZIP5, which is highly expressed in persimmon fruit. We also showed that ectopic DkbZIP5 overexpression in persimmon calluses induced the up-regulation of DkMyb4 and the resultant PA biosynthesis. In addition, a detailed molecular characterization using the electrophoretic mobility shift assay and transient reporter assay indicated that DkbZIP5 recognized ABA-responsive elements in the promoter region of DkMyb4 and acted as a direct regulator of DkMyb4 in an ABA-dependent manner. These results suggest that ABA signals may be involved in PA biosynthesis in persimmon fruit via DkMyb4 activation by DkbZIP5.

Highlights

Proanthocyanidins (PAs) are secondary metabolites that contribute to plant protection and crop quality
The expression of DkMyb2, which is another transcription factor (TF) involved in PA biosynthesis in persimmon (Akagi et al, 2010a), and four other Myb TFs expressed in persimmon fruit (Akagi et al, 2009b) did not show a significant difference between S-abscisic acid (ABA), abamine, and control sections in A- and NA-type cultivars (P . 0.05 for all sampling points; Supplemental Fig. S2)
As a factor providing a clue to the complex accumulation of PA in persimmon fruit, we found that ABA signaling can contribute to seasonal DkMyb4 expression and the resultant PA biosynthesis

Summary

Introduction

Proanthocyanidins (PAs) are secondary metabolites that contribute to plant protection and crop quality. A detailed molecular characterization using the electrophoretic mobility shift assay and transient reporter assay indicated that DkbZIP5 recognized ABA-responsive elements in the promoter region of DkMyb and acted as a direct regulator of DkMyb in an ABA-dependent manner These results suggest that ABA signals may be involved in PA biosynthesis in persimmon fruit via DkMyb activation by DkbZIP5. The biosynthesis of flavonoids, including PAs, is highly responsive to environmental conditions and can be regulated by seasonal signals. This is important because the phenological expression of some flavonoid-derived traits affects the quality of commercial crops. The signaling pathways involved in these responses remain to be elucidated

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