Plants exposed to repetitive touch or wind are generally shorter and stockier than sheltered plants. These mechanostimulus-induced developmental changes are termed thigmomorphogenesis and may confer resistance to subsequent stresses. An early response of Arabidopsis thaliana to touch or wind is the up-regulation of TCH (touch) gene expression. The signal transduction pathway that leads to mechanostimulus responses is not well defined. A role for ethylene has been proposed based on the observation that mechanostimulation of plants leads to ethylene evolution and exogenous ethylene leads to thigmomorphogenetic-like changes. To determine whether ethylene has a role in plant responses to mechanostimulation, we assessed the ability of two ethylene-insensitive mutants, etr1-3 and ein2-1, to undergo thigmomorphogenesis and TCH gene up-regulation of expression. The ethylene-insensitive mutants responded to wind similarly to the wild type, with a delay in flowering, decrease in inflorescence elongation rate, shorter mature primary inflorescences, more rosette paraclades, and appropriate TCH gene expression changes. Also, wild-type and mutant Arabidopsis responded to vibrational stimulation, with an increase in hypocotyl elongation and up-regulation of TCH gene expression. We conclude that the ETR1 and EIN2 protein functions are not required for the developmental and molecular responses to mechanical stimulation.

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.

The Arabidopsis_toucJ (TCH) genes are up-regulated i n response to various environmental stimuli, including touch, wind, and darkness. Previously, it was determined that TCHl encodes a calmodulin; TCHP and TCH3 encode calmodulin-related proteins. Here, we present the sequence and genomic organization of TCHR TCH3 is composed of three repeats; remarkably, the first two repeats share 94% sequence identity, including introns that are 99% identical. The conceptual TCHB product is 58 to 60% identical to known Arabidopsis calmodulins; however, unlike calmodulin, which has four Ca2+ binding sites, TCHB has six potential Ca2+ binding domains. TCHI 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 P-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, rootkhoot 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 TCHI 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, TCHB may perform a Ca2+-modulated function involved in generating changes in cells andlor tissues that result in greater strength or flexibility.

Expression of the Arabidopsis TCH genes is markedly upregulated in response to a variety of environmental stimuli including the seemingly innocuous stimulus of touch. Understanding the mechanism(s) and factors that control TCH gene regulation will shed light on the signaling pathways that enable plants to respond to environmental conditions. The TCH proteins include calmodulin, calmodulin-related proteins and a xyloglucan endotransglycosylase. Expression analyses and localization of protein accumulation indicates that the potential sites of TCH protein function include expanding cells and tissues under mechanical strain. We hypothesize that at least a subset of the TCH proteins may collaborate in cell wall biogenesis.

The Arabidopsis TCH genes were discovered as a consequence of their marked upregulation of expression in response to seemingly innocuous stimuli such as touch. Further analyses have indicated that these genes are upregulated by a variety of diverse stimuli. Understanding the mechanism(s) and factors that control TCH gene regulation will shed light on the signaling pathways that enable plants to respond to changing environmental conditions. The TCH proteins include calmodulin, calmodulin-related proteins and a xyloglucan endotransglycosylase. Expression analyses and localization of protein accumulation indicate that the potential sites of TCH protein function include expanding cells and tissues under mechanical strain. We hypothesize that the TCH proteins may collaborate in cell wall biogenesis.