I. Identification of thecis-regulatory elements of the Arabidopsis thaliana TCH3 gene. II. Developmental and molecular responses to touch stimulation in Arabidopsis mutants defective in ethylene responses

Plants respond to a variety of stimuli from their environment, including mechanical stimulation and changes in temperature or light. In Arabidopsis thaliana, morphological changes occur following touch stimulation, and this phenomenon is preceded by upregulation of expression of the TCH genes. The TCH3 transcription unit is 1522 base pairs (bp) and contains three 367-bp repeats which are highly identical. TCH3 encodes a 324 amino acid calcium-binding protein which is 58-60% identical to the Arabidopsis calmodulins and contains six potential Ca$\sp{2{+}},$ binding sites. To isolate the cis-regulatory elements responsible for upregulation of expression of TCH3 following touch, darkness, heat shock, and cold shock, transgenic plants harboring fusion genes containing 5$\sp\prime$ fragments of the TCH3 locus fused to the reporter gene uidA were created. A 43 bp sequence adjacent and 5$\sp\prime$ to the transcription unit of TCH3 is sufficient for induction of reporter gene expression following touch, darkness, and heat shock, and a 127 bp sequence which includes these 43 bp is sufficient for induction of expression in response to cold shock. Furthermore, it was determined that the 57-base 5$\sp\prime$ untranslated region of the TCH3 mRNA is important for post-transcriptionally regulated instability of the transcript. Sequences upstream of TCH3 direct reporter gene expression to the growing regions of roots, root/shoot junctions, apical meristems, leaf vasculature, and trichomes. Expression patterns of the fusion genes suggest TCH3 is required in regions of the plant which are subjected to stress, either applied externally or generated during development. It has been suggested that responses of plants to mechanical stimulation involves the plant hormone ethylene. To test this, Arabidopsis mutants defective in ethylene responses were examined for the ability to respond to touch. As in wild-type plants, the ethylene response mutants show reduced flowering stem elongation following touch stimulation and are capable of upregulation of TCH gene expression. This suggests that the loci defective in these ethylene response mutants are not required for developmental or molecular responses to touch stimulation in Arabidopsis