Xu W, Campbell P, Vargheese A K, Braam J
Department of Biochemistry and Cell Biology, Rice University, Houston, TX 77005-1892, USA.
Plant J. 1996 Jun;9(6):879-89. doi: 10.1046/j.1365-313x.1996.9060879.x.
Enzymes that modify cell wall components most likely play critical roles in altering size, shape, and physical properties of plant cells. Regulation of such modifying activity is expected to be important during morphogenesis and in eliciting developmental and physiological alterations that arise in response to environmental conditions. Previous work has shown that the Arabidopsis TCH4 gene encodes a xyloglucan endotransglycosylase (XET) which acts on the major hemicellulose of the plant cell wall. The expression of TCH4 is dramatically upregulated in response to several environmental stimuli (including touch, wind, darkness, heat shock, and cold shock) as well as the growth-enhancing hormones, auxin and brassinosteroids. This paper reports the presence of an extensive XET-related (XTR) gene family in Arabidopsis. In addition to TCH4, this family includes two previously identified genes, EXT and Meri-5, and at least five additional genes. The cDNAs of the XTR family share between 46 and 79% sequence identity and the predicted XTR proteins share from 37 to 84% identity. All eight proteins include potential N-terminal signal sequences and most have a conserved motif (DEIDFEFLG) that is also found in Bacillus beta-glucanase and may be important for enzyme activity. The members of the XTR gene family are differentially sensitive to environmental and hormonal stimuli. Magnitude and kinetics of regulation are distinct for the different genes. Differential regulation of expression of this complex gene family suggests a recruitment of related, yet distinct, cell wall-modifying enzymes that may control the properties of cell walls and tissues during development and in response to environmental cues.
修饰细胞壁成分的酶很可能在改变植物细胞的大小、形状和物理特性方面发挥关键作用。预计这种修饰活性的调节在形态发生过程中以及引发对环境条件作出反应而产生的发育和生理变化方面很重要。先前的研究表明，拟南芥TCH4基因编码一种木葡聚糖内转糖基酶（XET），该酶作用于植物细胞壁的主要半纤维素。TCH4的表达在受到几种环境刺激（包括触摸、风、黑暗、热休克和冷休克）以及生长促进激素、生长素和油菜素类固醇的刺激后会显著上调。本文报道了拟南芥中存在一个广泛的XET相关（XTR）基因家族。除了TCH4之外，这个家族还包括两个先前已鉴定的基因EXT和Meri-5，以及至少五个其他基因。XTR家族的cDNA序列同一性在46%至79%之间，预测的XTR蛋白同一性在37%至84%之间。所有八个蛋白都包含潜在的N端信号序列，并且大多数都有一个保守基序（DEIDFEFLG），该基序也存在于芽孢杆菌β-葡聚糖酶中，可能对酶活性很重要。XTR基因家族的成员对环境和激素刺激的敏感性不同。不同基因的调节幅度和动力学是不同的。这个复杂基因家族表达的差异调节表明募集了相关但不同的细胞壁修饰酶，这些酶可能在发育过程中以及对环境线索作出反应时控制细胞壁和组织的特性。
