Key Laboratory of National Forestry and Grassland Administration for Orchid Conservation and Utilization at College of Landscape Architecture, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
Fujian Colleges and Universities Engineering Research Institute of Conservation and Utilization of Natural Bioresources, College of Forestry, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
Plant Physiol. 2022 Jan 20;188(1):318-331. doi: 10.1093/plphys/kiab422.
Petals of the monocot Phalaenopsis aphrodite (Orchidaceae) possess conical epidermal cells on their adaxial surfaces, and a large amount of cuticular wax is deposited on them to serve as a primary barrier against biotic and abiotic stresses. It has been widely reported that subgroup 9A members of the R2R3-MYB gene family, MIXTA and MIXTA-like in eudicots, act to regulate the differentiation of conical epidermal cells. However, the molecular pathways underlying conical epidermal cell development and cuticular wax biosynthesis in monocot petals remain unclear. Here, we characterized two subgroup 9A R2R3-MYB genes, PaMYB9A1 and PaMYB9A2 (PaMYB9A1/2), from P. aphrodite through the transient overexpression of their coding sequences and corresponding chimeric repressors in developing petals. We showed that PaMYB9A1/2 function to coordinate conical epidermal cell development and cuticular wax biosynthesis. In addition, we identified putative targets of PaMYB9A1/2 through comparative transcriptome analyses, revealing that PaMYB9A1/2 acts to regulate the expression of cell wall-associated and wax biosynthetic genes. Furthermore, a chemical composition analysis of cuticular wax showed that even-chain n-alkanes and odd-chain primary alcohols are the main chemical constituents of cuticular wax deposited on petals, which is inconsistent with the well-known biosynthetic pathways of cuticular wax, implying a distinct biosynthetic pathway occurring in P. aphrodite flowers. These results reveal that the function of subgroup 9A R2R3-MYB family genes in regulating the differentiation of epidermal cells is largely conserved in monocots and dicots. Furthermore, both PaMYB9A1/2 have evolved additional functions controlling the biosynthesis of cuticular wax.
单子叶植物蝴蝶兰（兰科）花瓣的腹面具有圆锥形的表皮细胞，大量的角质层蜡沉积在上面，作为抵抗生物和非生物胁迫的主要屏障。已经广泛报道，R2R3-MYB 基因家族的亚组 9A 成员，在真双子叶植物中的 MIXTA 和 MIXTA-like，作用是调节圆锥形表皮细胞的分化。然而，单子叶植物花瓣中圆锥形表皮细胞发育和角质层蜡生物合成的分子途径尚不清楚。在这里，我们通过在发育中的花瓣中转基因瞬时过表达其编码序列及其相应的嵌合体抑制剂，从蝴蝶兰中鉴定了两个亚组 9A R2R3-MYB 基因，PaMYB9A1 和 PaMYB9A2（PaMYB9A1/2）。我们表明 PaMYB9A1/2 协同调节圆锥形表皮细胞发育和角质层蜡生物合成。此外，我们通过比较转录组分析鉴定了 PaMYB9A1/2 的假定靶标，揭示了 PaMYB9A1/2 作用于调节细胞壁相关和蜡生物合成基因的表达。此外，对蜡质化学组成的分析表明，直链 n-烷烃和奇数链伯醇是沉积在花瓣上的蜡质的主要化学成分，这与众所周知的蜡质生物合成途径不一致，表明在蝴蝶兰花中存在一种独特的生物合成途径。这些结果表明，R2R3-MYB 家族基因亚组 9A 在调节表皮细胞分化中的功能在单子叶植物和真双子叶植物中基本保守。此外，PaMYB9A1/2 已经进化出控制角质层蜡生物合成的额外功能。
