In plants, changes in cell size and shape during development fundamentally depend upon the ability to synthesize and modify cell wall polysaccharides. The main classes of cell wall polysaccharides of terrestrial plants are cellulose, hemicelluloses, and pectins. Members of the Cellulose synthases (CESA) and Cellulose Synthase-Like (CSL) families encode glycosyltransferases that synthesize the β-1,4-linked glycan backbones of cellulose and most hemicellulosic polysaccharides that comprise plant cell walls. Cellulose microfibrils are the major load bearing components in plant cell walls, and are assembled from individual β-1,4-glucan polymers synthesized by cellulose synthase CESA proteins that are organized into multimeric complexes, called cellulose synthase complexes (CSCs) in the plant plasma membrane. During distinct modes of polarized cell wall deposition, such as in tip-growth that occurs during the formation of root hairs and pollen tubes, or de novo formation of cell plates during plant cytokinesis, newly synthesized cell wall polysaccharides are deposited in a restricted region of the cell. These processes requires the activity of members of the cellulose synthase-like D subfamily. However, while these CSLD polysaccharide synthases are essential, the nature of the polysaccharides they synthesize has remained elusive. Here, we use a combination of genetic rescue experiments with CSLD-CESA chimeric proteins, in vitro biochemical reconstitution, and supporting computational modeling and simulation, to demonstrate that CSLD3 is a UDP-glucose dependent β-1,4-glucan synthases that forms protein complexes displaying similar ultrastructural features to those formed by the cellulose synthase, CESA6.

在植物中，发育过程中细胞大小和形状的变化基本上取决于合成和修饰细胞壁多糖的能力。陆生植物的细胞壁多糖的主要类别是纤维素，半纤维素和果胶。纤维素合酶（CESA）和类似纤维素合酶（CSL）的成员编码糖基转移酶，该酶合成纤维素与构成植物细胞壁的大多数半纤维素多糖的β-1,4-连接的聚糖主链。纤维素微纤维是植物细胞壁中的主要负重成分，由纤维素合成酶CESA蛋白合成的单个β-1,4-葡聚糖聚合物组装而成，在植物血浆中被组织成多聚体复合物，称为纤维素合成酶复合物（CSC）。膜。在极化细胞壁沉积的不同模式中，例如在根毛和花粉管形成过程中发生的尖端生长，或在植物胞质分裂过程中从头形成细胞板时，新合成的细胞壁多糖会沉积在细胞的受限区域中。细胞。这些过程需要纤维素合酶样D亚家族成员的活性。但是，尽管这些CSLD多糖合酶是必不可少的，但它们合成的多糖的性质仍然难以捉摸。在这里，我们结合CSLD-CESA嵌合蛋白的基因拯救实验，体外生化重构以及支持的计算建模和模拟，证明CSLD3是UDP-葡萄糖依赖性β-1，