The fruit of the pomegranate (Punica granatum L.) is an important nutraceutical food rich in polyphenolic compounds, including hydrolysable tannins, anthocyanins and flavonols. Their composition varies according to cultivar, tissue and fruit development stage and is probably regulated by a combination of MYB and bHLH type transcription factors (TFs). In this study, metabolomics analysis during fruit developmental stages in the main pomegranate cultivars, Wonderful and Valenciana with contrasting colour of their ripe fruits, showed that flavonols were mostly present in flowers while catechins were highest in unripe fruits and anthocyanins in late fruit maturation stages. A novel MYB TF, PgMYB5-like, was identified, which differs from previously isolated pomegranate TFs by unique C-terminal protein motifs and lack of the amino-acid residues conserved among anthocyanins promoting MYBs. In both pomegranate cultivars the expression of PgMYB5-like was high at flowering stage, while it decreased during fruit ripening. A previously identified bHLH-type TF, PgbHLH, also showed high transcript levels at flowering stage in both cultivars, while it showed a decrease in expression during fruit ripening in cv. Valenciana, but not in cv. Wonderful. Functional analysis of both TFs was performed by agro-infiltration into Nicotiana benthamiana leaves. Plants infiltrated with the PgMYB5-like+PgbHLH combined construct showed a specific and significant accumulation of intermediates of the flavonoid pathway, especially dihydroflavonols, while anthocyanins were not produced. Thus, we propose a role for PgMYB5-like and PgbHLH in the first steps of flavonoid production in flowers and in unripe fruits. The expression patterns of these two TFs may be key in determining the differential flavonoid composition in both flowers and fruits of the pomegranate varieties Wonderful and Valenciana.

中文翻译：

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MYB5 样和 bHLH 影响石榴中的黄酮类成分

石榴果实 (Punica granatum L.) 是一种重要的营养食品，富含多酚类化合物，包括可水解单宁、花青素和黄酮醇。它们的组成因品种、组织和果实发育阶段而异，可能受 MYB 和 bHLH 型转录因子 (TF) 的组合调节。在这项研究中，主要石榴品种 Wonderful 和 Valenciana 果实发育阶段的代谢组学分析表明，黄酮醇主要存在于花中，而未成熟果实中的儿茶素含量最高，果实成熟后期的花青素含量最高。鉴定了一种新的 MYB TF，类似于 PgMYB5，它与以前分离的石榴 TF 不同，在于独特的 C 端蛋白质基序和缺乏促进 MYB 的花青素中保守的氨基酸残基。在两个石榴品种中，PgMYB5-like 的表达在开花期很高，而在果实成熟期则下降。先前鉴定的 bHLH 型 TF，PgbHLH，在两个品种的开花期也显示出高转录水平，而在 cv. 果实成熟期间它显示出表达减少。瓦伦西亚纳，但不在简历中。精彩的。两种 TF 的功能分析是通过农业渗透到本氏烟草叶中进行的。用 PgMYB5 样 + PgbHLH 组合构建体浸润的植物表现出类黄酮途径中间体的特异性和显着积累，尤其是二氢黄酮醇，而没有产生花青素。因此，我们提出了 PgMYB5 样和 PgbHLH 在花和未成熟果实中类黄酮生产的第一步中的作用。这两种 TF 的表达模式可能是确定石榴品种 Wonderful 和 Valenciana 的花和果实中不同类黄酮成分的关键。