Laboratory of Pomology, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
Plant Physiol. 2009 Dec;151(4):2028-45. doi: 10.1104/pp.109.146985. Epub 2009 Sep 25.
Proanthocyanidins (PAs) are secondary metabolites that contribute to the protection of the plant and also to the taste of the fruit, mainly through astringency. Persimmon (Diospyros kaki) is unique in being able to accumulate abundant PAs in the fruit flesh. Fruits of the nonastringent (NA)-type mutants lose their ability to produce PA at an early stage of fruit development, while those of the normal astringent (A) type remain rich in PA until fully ripened. The expression of many PA pathway genes was coincidentally terminated in the NA type at an early stage of fruit development. The five genes encoding the Myb transcription factor were isolated from an A-type cultivar (Kuramitsu). One of them, DkMyb4, showed an expression pattern synchronous to that of the PA pathway genes in A- and NA-type fruit flesh. The ectopic expression of DkMyb4 in kiwifruit (Actinidia deliciosa) induced PA biosynthesis but not anthocyanin biosynthesis. The suppression of DkMyb4 in persimmon calluses caused a substantial down-regulation of the PA pathway genes and PA biosynthesis. Furthermore, analysis of the DNA-binding ability of DkMyb4 showed that it directly binds to the MYBCORE cis-motif in the promoters of the some PA pathway genes. All our results indicate that DkMyb4 acts as a regulator of PA biosynthesis in persimmon and, therefore, suggest that the reduction in the DkMyb4 expression causes the NA-type-specific down-regulation of PA biosynthesis and resultant NA trait.
原花青素（PAs）是植物保护和果实口感的次生代谢物，主要通过涩味来实现。柿子（Diospyros kaki）是唯一一种能够在果肉中积累丰富原花青素的水果。非涩型（NA）突变体的果实从果实发育的早期就丧失了产生 PA 的能力，而正常涩型（A）果实则在完全成熟之前一直富含 PA。许多 PA 途径基因的表达在 NA 型中在果实发育的早期就巧合地终止了。从 A 型品种（Kuramitsu）中分离到编码 Myb 转录因子的 5 个基因。其中一个，DkMyb4，在 A 型和 NA 型果肉中的 PA 途径基因表达模式同步。DkMyb4 在猕猴桃（Actinidia deliciosa）中的异位表达诱导了 PA 生物合成，但不诱导花青素生物合成。DkMyb4 在柿子愈伤组织中的抑制导致 PA 途径基因和 PA 生物合成的大量下调。此外，对 DkMyb4 的 DNA 结合能力的分析表明，它直接结合到一些 PA 途径基因启动子中的 MYBCORE 顺式基序上。我们所有的结果表明，DkMyb4 作为柿子中 PA 生物合成的调节剂，因此，DkMyb4 表达的减少导致了 NA 型特有的 PA 生物合成下调和由此产生的 NA 性状。
