Sistrunk M L, Antosiewicz D M, Purugganan M M, Braam J
Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77251-1892.
Plant Cell. 1994 Nov;6(11):1553-65. doi: 10.1105/tpc.6.11.1553.
The Arabidopsis touch (TCH) genes are up-regulated in response to various environmental stimuli, including touch, wind, and darkness. Previously, it was determined that TCH1 encodes a calmodulin; TCH2 and TCH3 encode calmodulin-related proteins. Here, we present the sequence and genomic organization of TCH3. TCH3 is composed of three repeats; remarkably, the first two repeats share 94% sequence identity, including introns that are 99% identical. The conceptual TCH3 product is 58 to 60% identical to known Arabidopsis calmodulins; however, unlike calmodulin, which has four Ca2+ binding sites, TCH3 has six potential Ca2+ binding domains. TCH3 is capable of binding Ca2+, as demonstrated by a Ca(2+)-specific shift in electrophoretic mobility. 5' Fragments of the TCH3 locus, when fused to the beta-glucuronidase (GUS) reporter gene, are sufficient to confer inducibility of expression following stimulation of plants with touch or darkness. These TCH3 sequences also direct expression to growing regions of roots, vascular tissue, root/shoot junctions, trichomes, branch points of the shoot, and regions of siliques and flowers. The pattern of expression of the TCH3/GUS reporter genes most likely reflects expression of the native TCH3 gene, because immunostaining of the TCH3 protein shows similar localization. The tissue-specific expression of TCH3 suggests that expression may be regulated not only by externally applied mechanical stimuli but also by mechanical stresses generated during development. Consequently, TCH3 may perform a Ca(2+)-modulated function involved in generating changes in cells and/or tissues that result in greater strength or flexibility.
拟南芥触摸（TCH）基因会在包括触摸、风吹和黑暗在内的各种环境刺激下上调表达。此前已确定，TCH1编码一种钙调蛋白；TCH2和TCH3编码与钙调蛋白相关的蛋白质。在此，我们展示了TCH3的序列和基因组结构。TCH3由三个重复序列组成；值得注意的是，前两个重复序列的序列一致性为94%，包括内含子的一致性为99%。TCH3的概念性产物与已知的拟南芥钙调蛋白有58%至60%的一致性；然而，与具有四个Ca2+结合位点的钙调蛋白不同，TCH3有六个潜在的Ca2+结合结构域。TCH3能够结合Ca2+，这通过电泳迁移率的Ca(2+)特异性变化得以证明。TCH3基因座的5'片段与β-葡萄糖醛酸酶（GUS）报告基因融合后，足以在植物受到触摸或黑暗刺激后赋予表达诱导性。这些TCH3序列还将表达导向根的生长区域、维管组织、根/茎连接处、毛状体、茎的分支点以及角果和花的区域。TCH3/GUS报告基因的表达模式很可能反映了天然TCH3基因的表达情况，因为TCH3蛋白的免疫染色显示出类似的定位。TCH3的组织特异性表达表明，其表达可能不仅受外部施加的机械刺激调控，还受发育过程中产生的机械应力调控。因此，TCH3可能执行一种Ca(2+)调节的功能，参与产生细胞和/或组织的变化，从而导致更强的强度或更大的柔韧性。
