Xu Weitao, Peng Xiaoqun, Li Yiqi, Zeng Xinhuang, Yan Wei, Wang Changjian, Wang Cheng Rui, Chen Shunquan, Xu Chunjue, Tang Xiaoyan
Guangdong Provincial Key Laboratory of Biotechnology for Plant Development, School of Life Sciences, South China Normal University, Guangzhou, China.
Shenzhen Institute of Molecular Crop Design, Shenzhen, China.
Rice (N Y). 2024 Aug 29;17(1):54. doi: 10.1186/s12284-024-00730-y.
Pollen is encased in a robust wall that shields the male gametophyte from various stresses and aids in pollination. The pollen wall consists of gametophyte-derived intine and sporophyte-derived exine. The exine is mainly composed of sporopollenin, which is biopolymers of aliphatic lipids and phenolics. The process of exine formation has been the subject of extensive research, yet the underlying molecular mechanisms remain elusive. In this study, we identified a rice mutant of the OsSNDP4 gene that is impaired in pollen development. We demonstrated that OsSNDP4, a putative Sec14-nodulin domain protein, exhibits a preference for binding to phosphatidylinositol (3)-phosphate [PI(3)P], a lipid primarily found in endosomal and vacuolar membranes. The OsSNDP4 protein was detected in association with the endoplasmic reticulum (ER), vacuolar membranes, and the nucleus. OsSNDP4 expression was detected in all tested organs but was notably higher in anthers during exine development. Loss of OsSNDP4 function led to abnormal vacuole dynamics, inhibition in Ubisch body development, and premature degradation of cellular contents and organelles in the tapetal cells. Microspores from the ossndp4 mutant plant displayed abnormal exine formation, abnormal vacuole enlargement, and ultimately, pollen abortion. RNA-seq assay revealed that genes involved in the biosynthesis of fatty acid and secondary metabolites, the biosynthesis of lipid polymers, and exosome formation were enriched among the down-regulated genes in the mutant anthers, which correlated with the morphological defects observed in the mutant anthers. Base on these findings, we propose that OsSNDP4 regulates pollen development by binding to PI(3)P and influencing the dynamics of membrane systems. The involvement of membrane systems in the regulation of sporopollenin biosynthesis, Ubisch body formation, and exine formation provides a novel mechanism regulating pollen wall development.
花粉被包裹在一层坚固的壁中，这层壁可保护雄配子体免受各种压力并有助于授粉。花粉壁由配子体衍生的内壁和孢子体衍生的外壁组成。外壁主要由孢粉素组成，孢粉素是脂肪族脂质和酚类的生物聚合物。外壁形成过程一直是广泛研究的主题，但其潜在的分子机制仍然难以捉摸。在本研究中，我们鉴定了一个在花粉发育中受损的水稻OsSNDP4基因突变体。我们证明，OsSNDP4是一种假定的Sec14-结节蛋白结构域蛋白，表现出优先结合磷脂酰肌醇(3)-磷酸[PI(3)P]的特性，PI(3)P是一种主要存在于内体和液泡膜中的脂质。在与内质网(ER)、液泡膜和细胞核相关的位置检测到了OsSNDP4蛋白。在所有测试器官中均检测到OsSNDP4的表达，但在花粉外壁发育过程中的花药中表达明显更高。OsSNDP4功能的丧失导致液泡动态异常、乌氏体发育受到抑制以及绒毡层细胞中细胞内容物和细胞器的过早降解。ossndp4突变体植株的小孢子表现出外壁形成异常、液泡异常增大，最终导致花粉败育。RNA测序分析显示，参与脂肪酸和次生代谢物生物合成、脂质聚合物生物合成以及外泌体形成的基因在突变体花药中下调的基因中富集，这与在突变体花药中观察到的形态缺陷相关。基于这些发现，我们提出OsSNDP4通过结合PI(3)P并影响膜系统的动态来调节花粉发育。膜系统参与孢粉素生物合成、乌氏体形成和外壁形成的调节，为调节花粉壁发育提供了一种新机制。
