Xylan is the predominant hemicellulose in the primary cell walls of grasses, but its synthesis and interactions with other wall polysaccharides are complex and incompletely understood. To probe xylan biosynthesis, we generated CRISPR/Cas9 knockout and amiRNA knockdown lines of BdGT43B2, an ortholog of the wheat TaGT43‐4 xylan synthase scaffolding protein in the IRX14 clade, in Brachypodium distachyon. Knockout of BdGT43B2 caused stunting and premature death in Brachypodium seedlings. Immunofluorescence labeling of xylans was greatly reduced in homozygous knockout BdGT43B2 mutants, whereas cellulose labeling was unchanged or slightly increased. Biochemical analysis showed reductions in digestible xylan in knockout mutant walls, and cell size was smaller in knockout leaves. BdGT43B2 knockdown plants appeared morphologically normal as adults, but showed slight reductions in seedling growth and small decreases in xylose content in isolated cell walls. Immunofluorescence labeling of xylan and cellulose staining was both reduced in BdGT43B2 knockdown plants. Together, these data indicate that BdGT43B2 functions in the synthesis of a form of xylan that is required for seedling growth and survival in Brachypodium distachyon.

中文翻译：

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BdGT43B2 在木聚糖生物合成中发挥作用，对于二穗短柄草幼苗的存活至关重要。

木聚糖是草类初生细胞壁中的主要半纤维素，但其合成及其与其他细胞壁多糖的相互作用非常复杂且尚未完全了解。为了探究木聚糖生物合成，我们在二穗短柄草中生成了BdGT43B2的 CRISPR/Cas9 敲除和 amiRNA 敲除系，BdGT43B2 是二穗短柄草IRX14进化枝中小麦TaGT43-4木聚糖合酶支架蛋白的直系同源物。BdGT43B2的敲除会导致短柄草幼苗发育迟缓和过早死亡。在纯合敲除BdGT43B2突变体中，木聚糖的免疫荧光标记大大减少，而纤维素标记则没有变化或略有增加。生化分析显示，敲除突变体壁中可消化的木聚糖减少，敲除叶片中的细胞尺寸更小。BdGT43B2敲除植物在成年时形态正常，但幼苗生长略有减少，分离细胞壁中木糖含量略有下降。在BdGT43B2敲低植物中，木聚糖和纤维素染色的免疫荧光标记均减少。总之，这些数据表明BdGT43B2在二穗短柄草幼苗生长和存活所需的一种木聚糖的合成中发挥作用。