School of BioSciences, University of Melbourne, Parkville, VIC 3052, Australia.
La Trobe Institute for Sustainable Agriculture and Food, Department of Animal, Plant and Soil Science, La Trobe University, Bundoora, VIC 3086, Australia.
Plant Physiol. 2023 May 2;192(1):119-132. doi: 10.1093/plphys/kiad097.
The role of glycoproteins as key cell surface molecules during development and stress is well established; yet, the relationship between their structural features and functional mechanisms is poorly defined. FASCICLIN-LIKE ARABINOGALACTAN PROTEINs (FLAs), which impact plant growth and development, are an excellent example of a glycoprotein family with a complex multidomain structure. FLAs combine globular fasciclin-like (FAS1) domains with regions that are intrinsically disordered and contain glycomotifs for directing the addition of O-linked arabinogalactan (AG) glycans. Additional posttranslational modifications on FLAs include N-linked glycans in the FAS1 domains, a cleaved signal peptide at the N terminus, and often a glycosylphosphatidylinositol (GPI) anchor signal sequence at the C terminus. The roles of glycosylation, the GPI anchor, and FAS1 domain functions in the polysaccharide-rich extracellular matrix of plants remain unclear, as do the relationships between them. In this study, we examined sequence-structure-function relationships of Arabidopsis (Arabidopsis thaliana) FLA11, demonstrated to have roles in secondary cell wall (SCW) development, by introducing domain mutations and functional specialization through domain swaps with FLA3 and FLA12. We identified FAS1 domains as essential for FLA function, differentiating FLA11/FLA12, with roles in SCW development, from FLA3, specific to flowers and involved in pollen development. The GPI anchor and AG glycosylation co-regulate the cell surface location and release of FLAs into cell walls. The AG glycomotif sequence closest to the GPI anchor (AG2) is a major feature differentiating FLA11 from FLA12. The results of our study show that the multidomain structure of different FLAs influences their subcellular location and biological functions during plant development.
糖蛋白作为发育和应激过程中关键的细胞表面分子的作用已得到充分证实；然而，其结构特征与功能机制之间的关系还没有得到很好的定义。影响植物生长和发育的纤维蛋白样阿拉伯半乳糖蛋白（FLAs）是具有复杂多结构域结构的糖蛋白家族的一个极好范例。FLAs 结合了球状的纤维蛋白样（FAS1）结构域和富含糖基的区域，这些区域具有内在的无序性，并包含指导 O-连接阿拉伯半乳糖（AG）聚糖添加的糖基基序。FLAs 的其他翻译后修饰包括 FAS1 结构域中的 N-连接聚糖、N 端切割的信号肽以及 C 端的糖基磷脂酰肌醇（GPI）锚信号序列。糖基化、GPI 锚和 FAS1 结构域在富含多糖的植物细胞外基质中的作用仍不清楚，它们之间的关系也不清楚。在这项研究中，我们通过与 FLA3 和 FLA12 进行结构域交换，引入结构域突变和功能特化，研究了拟南芥（Arabidopsis thaliana）FLA11 的序列-结构-功能关系，证明其在次生细胞壁（SCW）发育中具有作用。我们确定 FAS1 结构域是 FLA 功能所必需的，将 FLA11/FLA12 与 SCW 发育相关的 FLA3 区分开来，后者特异性地参与花的发育和花粉的发育。GPI 锚和 AG 糖基化共同调节 FLA 的细胞表面定位和向细胞壁的释放。与 GPI 锚最近的 AG 糖基基序（AG2）是区分 FLA11 和 FLA12 的主要特征。我们的研究结果表明，不同 FLA 的多结构域结构影响它们在植物发育过程中的亚细胞定位和生物学功能。
