Song Yunyun, Tang Yongyan, Liu Lingtong, Xu Yunyuan, Wang Tai
Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, China.
College of Life Science, University of Chinese Academy of Sciences, Beijing, 100093, China.
Plant J. 2022 Sep;111(5):1283-1295. doi: 10.1111/tpj.15887. Epub 2022 Jul 12.
Pollen exine is composed of finely-organized nexine, bacula and tectum, and is crucial for pollen viability and function. Pollen exine development involves a complicated molecular network that coordinates the interaction between pollen and tapetal cells, as well as the biosynthesis, transport and assembly of sporopollenin precursors; however, our understanding of this network is very limited. Here, we report the roles of PEM1, a member of methyl-CpG-binding domain family, in rice pollen development. PEM1 expressed constitutively and, in anthers, its expression was detectable in tapetal cells and pollen. This predicted PEM1 protein of 240 kDa had multiple epigenetic-related domains. pem1 mutants exhibited abnormal Ubisch bodies, delayed exine occurrence and, finally, defective exine, including invisible bacula, amorphous and thickened nexine and tectum layer structures, and also had the phenotype of increased anther cuticle. The mutation in PEM1 did not affect the timely degradation of tapetum. Lipidomics revealed much higher wax and cutin contents in mutant anthers than in wild-type. Accordingly, this mutation up-regulated the expression of a set of genes implicated in transcriptional repression, signaling and diverse metabolic pathways. These results indicate that PEM1 mediates Ubisch body formation and pollen exine development mainly by negatively modulating the expression of genes. Thus, the PEM1-mediated molecular network represents a route for insights into mechanisms underlying pollen development. PEM1 may be a master regulator of pollen exine development.
花粉外壁由精细组织的内壁、基粒棒和覆盖层组成，对花粉的活力和功能至关重要。花粉外壁发育涉及一个复杂的分子网络，该网络协调花粉与绒毡层细胞之间的相互作用，以及孢粉素前体的生物合成、运输和组装；然而，我们对这个网络的了解非常有限。在这里，我们报道了甲基-CpG结合域家族成员PEM1在水稻花粉发育中的作用。PEM1组成型表达，在花药中，其表达在绒毡层细胞和花粉中均可检测到。预测的240 kDa的PEM1蛋白具有多个与表观遗传相关的结构域。pem1突变体表现出乌氏体异常、外壁出现延迟，最终外壁有缺陷，包括不可见的基粒棒、无定形且增厚的内壁和覆盖层结构，并且还具有花药角质层增加的表型。PEM1的突变不影响绒毡层的及时降解。脂质组学分析显示，突变体花药中的蜡质和角质含量比野生型高得多。因此，这种突变上调了一组与转录抑制、信号传导和多种代谢途径相关的基因的表达。这些结果表明PEM1主要通过负向调节基因表达来介导乌氏体形成和花粉外壁发育。因此，PEM1介导的分子网络代表了一条深入了解花粉发育机制的途径。PEM1可能是花粉外壁发育的主要调节因子。
