Isolation and characterisation of a Myb transcription factor DkPA1 related to proanthocyanidin biosynthesis in C-PCNA and non-PCNA persimmon (Diospyros kaki Thunb.) fruit

Proanthocyanidins (PAs) are secondary metabolites that contribute to important plant traits like fruit astringency. Persimmon (Diospyros kaki Thunb.) is unique for accumulating abundant PAs in its fruit flesh. Two non-astringent-type mutants, namely, Japanese pollination-constant and non-astringent (J-PCNA) and Chinese PCNA (C-PCNA), were unable to accumulate PA naturally on the tree before harvest. It was clear that the decreased expression profile of a Myb transcription factor (TF) DkMyb4 in persimmon fruits results in the PCNA trait in J-PCNA mutant. However, the mechanism leading to the PCNA trait in C-PCNA mutant remains unclear. In this study, with the purpose of figuring out whether or not there was a certain Myb TF resulting in PCNA trait in C-PCNA mutant, a gene homologous to DkMyb4 was isolated from C-PCNA cultivar ‘Luotian-tianshi’, named DkPA1. Bioinformatics analysis showed that DkPA1 shared high similarity to DkMyb4 in amino acid level, and that DkPA1 was phylogenetically closer to PA-related Myb TFs. Expression pattern of DkPA1 coincided with expression of PA pathway genes, also consistent with PA accumulation model in both C-PCNA and non-PCNA fruit during fruit development. Though being absent in J-PCNA, we found there were MYBCORE cis-motifs in promoter of PA pathway Leucoanthocyanidin reductase (DkLAR) gene isolated from C-PCNA and non-PCNA, which was reported as a key cis-element for PA biosynthesis and target of Myb TFs. These results suggested that DkLAR was regulated by DkPA1 in C-PCNA and non-PCNA, it played much more important role in C-PCNA and non-PCNA PA biosynthesis than that in J-PCNA.