Zhengzhou Fruit Research Institute, Chinese Academy of Agricultural Sciences (CAAS), Zhengzhou, 450009, China.
The University of Queensland , St Lucia, QLD 4072, Australia.
Plant Physiol Biochem. 2019 Jun;139:379-388. doi: 10.1016/j.plaphy.2019.01.033. Epub 2019 Mar 5.
The pomegranate, Punica granatum L., which has been cultivated since antiquity, is known to be a superfruit, possessing an array of functional anti-oxidants and various other health benefits. The hardness of pomegranate seeds is an important indicator of fruit quality, which in turn affects economic value and market demand. However, the molecular mechanism underlying pomegranate seed hardness remains to be fully understood. In this study, we found a positive correlation between seed hardness and lignin content in two pomegranate varieties: "Tunisia" and "Sanbai". Specifically, genes associated with lignin biosynthesis were differentially expressed in soft-seed and hard-seed pomegranate varieties. Among these differential genes, we cloned and characterized the NAC transcription factor PgSND1-like. Sequence alignment found a single base replacement at the 166-bp position of CDS in the PgSND1-like gene from "Tunisia" and "Sanbai". Both PgSND1-like (Sanbai) and PgSND1-like (Tunisia) proteins are localized in the cell nucleus and have a transcription activation domain in the C-terminus. Yeast two-hybrid analysis indicated that PgSND1-like protein interacts with itself to form a homodimer. Overexpression of PgSND1-like (Sanbai) in Arabidopsis showed a higher lignin content in inflorescence stem and mature seed compared with wild-type Arabidopsis. Accordingly, the expression levels of several lignin biosynthesis-associated genes were upregulated in stem cells and mature seeds of transgenic plants. However, PgSND1-like (Tunisia) transgenic Arabidopsis showed no phenotypic differences with wild-type Arabidopsis. Taken together, we suggest that PgSND1-like may regulate at least two different functions in two pomegranate varieties, promoting lignin biosynthesis and seed hardness of pomegranate.
石榴，Punica granatum L.，自古就有种植，被认为是一种超级水果，具有一系列功能性抗氧化剂和各种其他健康益处。石榴籽的硬度是果实品质的一个重要指标，进而影响经济价值和市场需求。然而，石榴籽硬度的分子机制尚未完全了解。在这项研究中，我们发现两个石榴品种“突尼斯”和“三白”的种子硬度与木质素含量呈正相关。具体来说，与木质素生物合成相关的基因在软籽和硬籽石榴品种中差异表达。在这些差异基因中，我们克隆并表征了 NAC 转录因子 PgSND1-like。序列比对发现，“突尼斯”和“三白”的 PgSND1-like 基因 CDS 第 166 位有一个碱基替换。PgSND1-like（三白）和 PgSND1-like（突尼斯）蛋白都定位于细胞核内，C 端具有转录激活结构域。酵母双杂交分析表明，PgSND1-like 蛋白自身相互作用形成同源二聚体。在拟南芥中过表达 PgSND1-like（三白），与野生型拟南芥相比，花序茎和成熟种子中的木质素含量更高。因此，转基因植物的茎细胞和成熟种子中几个木质素生物合成相关基因的表达水平上调。然而，PgSND1-like（突尼斯）转基因拟南芥与野生型拟南芥没有表现出明显的表型差异。综上所述，我们认为 PgSND1-like 可能在两个不同的石榴品种中调节至少两种不同的功能，促进木质素生物合成和石榴籽的硬度。
