在植物细胞中，细胞壁与细胞质膜和细胞骨架形成一个在结构上连续的功能单位连接着细胞内外，参与物质交换和信号交流，在植物生长发育和器官塑形等过程中发挥至关重要的作用。CSI1在细胞质膜定位的纤维素合酶复合体和周质微管之间起连接作用，是建立细胞壁-细胞质膜-细胞骨架连续体的重要蛋白之一。目前，关于CSI1参与调控纤维素合成的功能和分子机制已经较为清晰，但关于CSI1在细胞壁-细胞质膜-细胞骨架连续体中的作用及其生理学意义都还有待深入研究。

本论文综合利用遗传学、分子生物学和细胞生物学等技术手段系统分析了拟南芥CSI1的功能，重点解析了其在茎顶端分生组织塑形中的作用。研究结果显示，CSI1的功能缺失突变体csi1-3和pom2-4的茎顶端分生组织弧度显著低于野生型植株，并且弧度的降低并不是由细胞数量的改变引起的，而是由于细胞形态和细胞分裂角度改变导致的。通过荧光标记观察到，csi1-3茎顶端分生组织中处于分裂期的细胞数量相比对照显著减少，细胞分裂素含量也显著降低。进一步的研究表明，csi1-3和野生型茎顶端分生组织微管的各向异性值并没有显著的差异，但csi1-3中微管的动态性减弱；进行细胞损伤实验时，csi1-3茎顶端分生组织损伤周围细胞微管方向转变比野生型植株快，暗示着CSI1可能参与抑制微管对机械力的过度响应。区域和细胞层特异性回补植株的实验表明，只有自身启动子表达的CSI1回补植株能够回补csi1-3茎顶端分生组织弧度降低的表型，由此证明茎顶端分生组织的弧度并不是由单一区域控制的，而是由多区域共同控制。此外，根小柱细胞数量减少导致csi1-3植株向重力性缺陷。csi1-3花粉粒的大小、花粉管长度和花粉管延伸速率与野生型存在显著性差异，证明CSI1在控制花粉粒大小和花粉管的生长过程中起到重要作用。

上述研究结果表明，CSI1可能通过抑制细胞周质微管对机械力的过度响应来参与调控茎顶端分生组织的形态建成，同时在植物的向重力性和花粉萌发及延伸过程中发挥重要功能。

In plant cells, cell wall, plasma membrane and cytoskeleton form a structurally continuous unit, which connects the inside and outside of cells and participates in material and signal exchange. The cell wall-plasma membrane-cytoskeleton continuum plays an important role in plant growth development and organ morphogenesis. CSI1, which links plasma membrane-localized cellulose synthase complex and microtubule, is one of the important proteins for the establishment of cell wall- plasma membrane -cytoskeleton continuum. The functions of CSI1 in regulating cellulose synthesis have been detailed elucidated. However, the roles of CSI1 in cell wall-plasma membrane-cytoskeleton continuum and its physiological significance still need further investigation.

Here, by combination of genetics, molecular biology and cell biology techniques, the function of Arabidopsis CSI1 in modulating the morphogenesis of shoot apical meristem (SAM) was systematically analyzed. The results showed that the curvature of SAM was significantly reduced in two mutants of CSI1, csi1-3 and pom2-4, compared with that of wild-type plants. The decrease of meristem curvature was not caused by the change of cell number, but by the change of cell morphology and cell division angle. The number of cells at division stage in csi1-3 meristem was significantly reduced compared with the control. Consistently, the content of cytokinin was significantly reduced compared with control. Further studies revealed that there was no significant difference in the anisotropy of microtubules between csi1-3 and wild-type plants, but the dynamics of microtubules in csi1-3 mutant was decreased; In cell ablation experiment, the direction of microtubules around the damaged region changed faster in csi1-3 meristem than that in wild-type plants, suggesting that CSI1 might be involved in inhibiting the excessive response of microtubules to mechanical force. Native and several region and cell layer specific promoters were employed to drive the expression of CSI1 in csi1-3 mutant background and only the native promoter-driven construct successfully restored the SAM curvature phenotype of csi1-3. These data suggested that the SAM curvature was most likely controlled by multiple regions or layers rather than a single region or layer. Further analysis revealed that the decrease in the number of root columnar cells resulted in the defect of gravitropism of csi1-3 plants. There were significant differences in pollen grain size, pollen tube length and pollen tube elongation rate between csi1-3 and wild type, which indicated that CSI1 was also involved in controlling pollen grain size and pollen tube elongation.

In conclusion, CSI1 may be involved in the regulating SAM morphogenesis through inhibiting over-response of plants to mechanical stress. It also played important roles in root gravitropism and in the control of pollen grain size and pollen tube elongation.