Similar to cellulose synthases (CESAs), cellulose synthase–like D (CSLD) proteins synthesize β-1,4-glucan in plants. CSLDs are important for tip growth and cytokinesis, but it was unknown whether they form membrane complexes in vivo or produce microfibrillar cellulose. We produced viable CESA-deficient mutants of the moss Physcomitrium patens to investigate CSLD function without interfering CESA activity. Microscopy and spectroscopy showed that CESA-deficient mutants synthesize cellulose microfibrils that are indistinguishable from those in vascular plants. Correspondingly, freeze-fracture electron microscopy revealed rosette-shaped particle assemblies in the plasma membrane that are indistinguishable from CESA-containing rosette cellulose synthesis complexes (CSCs). Our data show that proteins other than CESAs, most likely CSLDs, produce cellulose microfibrils in P. patens protonemal filaments. The data suggest that the specialized roles of CSLDs in cytokinesis and tip growth are based on differential expression and different interactions with microtubules and possibly Ca 2+ , rather than structural differences in the microfibrils they produce.

中文翻译：

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植物中纤维素微纤维生物合成的另一种途径


与纤维素合酶 （CESA） 类似，纤维素合酶样 D （CSLD） 蛋白在植物中合成 β-1,4-葡聚糖。CSLD 对尖端生长和胞质分裂很重要，但尚不清楚它们是否在体内形成膜复合物或产生微纤维纤维素。我们生产了苔藓 Physcomitrium patens 的活 CESA 缺陷突变体，以在不干扰 CESA 活性的情况下研究 CSLD 功能。显微镜和光谱学表明，CESA 缺陷突变体合成的纤维素微纤维与维管植物中的微纤维无法区分。相应地，冷冻断裂电子显微镜显示质膜中的莲座状颗粒组装体与含有 CESA 的玫瑰花座纤维素合成复合物 （CSC） 无法区分。我们的数据显示，除 CESA 以外的蛋白质，很可能是 CSLDs，在 P. patens 质子丝中产生纤维素微纤维。数据表明，CSLD 在胞质分裂和尖端生长中的特殊作用是基于差异表达和与微管（可能还有 Ca 2+）的不同相互作用，而不是它们产生的微原纤维的结构差异。