CELLULAR-LOCALIZATION OF THE CA2+ BINDING TCH3 PROTEIN OF ARABIDOPSIS

TCH3 is an Arabidopsis touch (TCH) gene isolated as a result of its st rong and rapid upregulation in response to mechanical stimuli, such as touch and wind. TCH3 encodes an unusual calcium ion-binding protein t hat is closely related to calmodulin but has the potential to bind six calcium ions. Here it is shown that TCH3 shows a restricted pattern o f accumulation during Arabidopsis vegetative development. These data p rovide insight into the endogenous signals that may regulate TCH3 expr ession and the sites of TCH3 action. TCH3 is abundant in the shoot api cal meristem, vascular tissue, the root columella and pericycle cells that give rise to lateral roots. In addition, TCH3 accumulation in cel ls of developing shoots and roots closely correlates with the process of cellular expansion. Following wind stimulation, TCH3 becomes more a bundant in specific regions including the branchpoints of leaf primord ia and stipules, pith parenchyma, and the vascular tissue. The consequ ences of TCH3 upregulation by wind are therefore spatially restricted and TCH3 may function at these sites to modify cell or tissue characte ristics following mechanical stimulation. Because TCH3 accumulates spe cifically in cells and tissues that are thought to be under the influe nce of auxin, auxin levels may regulate TCH3 expression during develop ment. TCH3 is upregulated in response to low levels of exogenous indol e-3-acetic acid (IAA), but not by inactive auxin-related compounds. Th ese results suggest that TCH3 protein may play roles in mediating phys iological responses to auxin and mechanical environmental stimuli.