Cellulose synthesis is essential for plant morphology, water transport and defense, and provides raw material for biomaterials and fuels. Cellulose is produced at the plasma membrane by Cellulose Synthase (CESA) complexes (CSCs). CSCs are assembled in the endomembrane system and then trafficked from the Golgi apparatus and trans-Golgi Network (TGN) to the plasma membrane. Since CESA enzymes are only active in the plasma membrane, control of CSC secretion is a critical step in the regulation of cellulose synthesis. However, the regulatory framework for CSC secretion is not clarified. In this study, we identify members of a family of seven transmembrane domain-containing proteins (7TMs) as important for cellulose production during cell wall integrity stress. 7TM proteins are often associated with guanine nucleotide-binding (G) protein signalling and mutants in several of the canonical G protein complex components phenocopied the 7tm mutant plants. Unexpectedly, the 7TM proteins localized to the Golgi apparatus/TGN where they interacted with the G protein complex. Here, the 7TMs and G proteins regulated CESA trafficking, but did not affect general protein secretion. Furthermore, during cell wall stress, 7TM localization was biased towards small CESA-containing vesicles, specifically associated with CSC trafficking. Our results thus outline how a G protein-coupled module regulates CESA trafficking and reveal that defects in this process lead to exacerbated responses upon exposure to cell wall integrity stress.

中文翻译：

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AG蛋白偶联受体样模块调节拟南芥内膜系统中纤维素合酶的分泌

纤维素合成对于植物形态，水的运输和防御至关重要，并为生物材料和燃料提供了原材料。纤维素是由纤维素合酶（CESA）复合物（CSC）在质膜上产生的。CSC在膜系统中组装，然后从高尔基体和反高尔基体网络（TGN）转运到质膜。由于CESA酶仅在质膜中起作用，因此控制CSC分泌是调节纤维素合成的关键步骤。但是，尚不清楚CSC分泌的调控框架。在这项研究中，我们确定了一个家族的七个跨膜域的蛋白质（7TMs）的成员对于细胞壁完整性压力期间的纤维素生产很重要。7TM蛋白通常与鸟嘌呤核苷酸结合（G）蛋白信号传导和表型7tm突变植物的几种典型G蛋白复合物组分中的突变体相关。出乎意料的是，7TM蛋白位于高尔基体/ TGN中，在那里它们与G蛋白复合物相互作用。在这里，7TM和G蛋白调节CESA的运输，但不影响一般蛋白的分泌。此外，在细胞壁应激期间，7TM定位偏向于包含CESA的小囊泡，特别是与CSC转运有关。因此，我们的研究结果概述了G蛋白偶联模块如何调控CESA转运，并揭示了该过程中的缺陷会导致细胞壁完整性应力下的反应加剧。