GPI锚定糖蛋白SKU5和SKS1协同调控根细胞壁纤维素合成的机制研究

Cell wall is composed of the polysaccharides cellulose, hemicellulose, pectin and lignin. Especially cellulose and lignin are the major components of forest wood, being the important renewable biological resources. In the aspect of cellulose biosynthesis, the function of Cellulose Synthases (CESAs) and the related proteins have been intensively studied, while plenty of questions are unclear. Besides, many GPI-anchored glycoproteins have been reported to be involved in cellulose formation, while the mechanism of GPI-anchored domain in this process is still unknown. In our project, we used Arabidopsis root as model system, and we searched the highly co-expressed genes with CESAs etc. We obtained SKU5 gene which belongs to GPI-anchored glycoprotein. Our preliminary data showed sku5 sks1 double mutant (SKS1 is a homolog of SKU5) decreases cellulose level and exhibits cell wall defects. Further, we plan to explore the mechanisms by which SKU5 and SKS1 redundantly regulate cellulose formation, leading to root cell expansion. Meanwhile, according to the key roles of glycoproteins in cellulose synthesis, we try to gain insight into the function of GPI-anchor glycosylated domain in cell wall formation. Cell wall-related genes of this project can be used for the tree genetics and breeding, hopefully to provide a theoretical basis for renewable biological resources.

细胞壁的主要成分是纤维素、半纤维素、果胶和木质素，其中纤维素和木质素是森林木材的重要成分，是地球上可再生的重要生物资源。在纤维素合成过程中，合成酶CESAs发挥关键功能，然而还有许多问题尚未解决；此外，多个GPI锚定的糖基化蛋白已被报道参与纤维素合成，然而GPI修饰在纤维素合成过程中的作用尚不清楚。本课题以根为研究模型，从拟南芥共表达的基因数据库出发，获得了与CESAs等共表达得分较高的GPI糖基化蛋白SKU5。初步数据表明sku5sks1双突变体（SKS1为SKU5同源基因）表现为细胞壁纤维素下降以及细胞壁缺陷相关表型。我们计划以根形态建成为模型，围绕SKU5与SKS1冗余协同调控细胞壁纤维素组成，合理的设计实验并阐明机制；同时，进一步挖掘GPI糖基化链在纤维素合成过程中的功能。本项目中获得的调控细胞壁的重要功能蛋白有希望运用于林木生产中，为改善林木获得可再生生物能源提供理论基础。

铁对植物的生长和发育至关重要，在叶绿素合成、有氧呼吸、生物固氮等途径均发挥关键的作用，是许多重要的细胞过程中必不可少的辅助因子。缺铁影响植物的生长发育，而过量的铁又具有细胞毒性，因而在植物体内存在精细的调控模型来维持铁元素的稳态。本课题的研究结论提出了SKU5和其同源蛋白SKS1介导的铁稳态的在根生长发育过程中的精细调控模型。缺失SKU5和SKS1的sku5 sks1双突变体表现为根粗短，根细胞分裂异常，外皮层和皮层交界区域的细胞壁增厚和异常凸起等表型。通过遗传检测和细胞生物学观测，本课题证实SKU5是根尖吸收铁的重要响应蛋白，参与了铁从根细胞的外皮层向皮层、维管束方向的吸收。由于铁无法正常吸收进入突变体根中，sku5 sks1在外皮层-皮层交界区域的细胞壁沉积大量的铁元素。进而sku5 sks1在外皮层-皮层交界区域积累大量的活性氧，导致细胞壁松散。因此，本课题进一步证实了SKU5通过调节细胞表面的活性氧累积，参与过量铁沉积引发的细胞毒性调控。综上所述，本项目的研究结论为植物根细胞严格的摄取和调控铁元素的吸收利用奠定了理论基础。