Plant cell walls are essential for growth. The cell wall hemicellulose xyloglucan (XyG) is produced in the Golgi apparatus before secretion. Loss of the Arabidopsis galactosyltransferase MURUS3 (MUR3) decreases XyG d-galactose side chains and causes intracellular aggregations and dwarfism. It is unknown how changing XyG synthesis can broadly impact organelle organization and growth. We show that intracellular aggregations are not unique to mur3 and are found in multiple mutant lines with reduced XyG D-galactose side chains. mur3 aggregations disrupt subcellular trafficking and induce formation of intracellular cell-wall-like fragments. Addition of d-galacturonic acid onto XyG can restore growth and prevent mur3 aggregations. These results indicate that the presence, but not the composition, of XyG side chains is essential, likely by ensuring XyG solubility. Our results suggest that XyG polysaccharides are synthesized in a highly substituted form for efficient secretion and then later modified by cell-wall-localized enzymes to fine-tune cell wall properties.

植物细胞壁对于生长至关重要。细胞壁半纤维素木葡聚糖 (XyG) 在分泌前在高尔基体中产生。拟南芥半乳糖基转移酶 MURUS3 (MUR3) 的缺失会减少 XyG d-半乳糖侧链并导致细胞内聚集和侏儒症。目前尚不清楚改变 XyG 合成如何广泛影响细胞器的组织和生长。我们发现细胞内聚集并不是Mur3所独有的，并且在 XyG D-半乳糖侧链减少的多个突变系中也发现了这种情况。 Mur3聚集会破坏亚细胞运输并诱导细胞内细胞壁样片段的形成。在 XyG 上添加d-半乳糖醛酸可以恢复生长并防止mur3聚集。这些结果表明，XyG 侧链的存在（而非其组成）至关重要，这可能是为了确保 XyG 的溶解度。我们的结果表明，XyG 多糖以高度取代的形式合成，以实现有效分泌，然后通过细胞壁定位酶进行修饰，以微调细胞壁特性。