ARABIDOPSIS TCH3 ENCODES A NOVEL CA2-PROTEIN AND SHOWS ENVIRONMENTALLY-INDUCED AND TISSUE-SPECIFIC REGULATION( BINDING)

The Arabidopsis touch (TCH) genes are up-regulated in response to vari ous environmental stimuli, including touch, wind, and darkness. Previo usly, 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; remark ably, the first two repeats share 94% sequence identity, including int rons 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+ bindi ng domains. TCH3 is capable of binding Ca2+, as demonstrated by a Ca2-specific shift in electrophoretic mobility. 5' Fragments of the TCH3 locus, when fused to the beta-glucuronidase (GUS) reporter gene, are s ufficient to confer inducibility of expression following stimulation o f plants with touch or darkness. these TCH3 sequences also direct expr ession to growing regions of roots, vascular tissue, root/shoot juncti ons, trichomes, branch points of the shoot, and regions of siliques an d flowers. The pattern of expression of the TCH3/GUS reporter genes mo st likely reflects expression of the native TCH3 gene, because immunos taining of the TCH3 protein shows similar localization. The tissue-spe cific 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 Ca2+-modulated function involved in generating changes in cells and/ or tissues that result in greater strength or flexibility.