A multi-responsive gene encoding 1-aminocyclopropane-1-carboxylate synthase (ACS6) in mature Arabidopsis leaves

Physiological and biochemical studies have provided evidence that mechanica l strain (touch)-induced modifications in plant growth and development may be due to ethylene. In order to better understand the involvement of ethyle ne in touch-induced responses, we identified and characterized an Arabidops is cDNA (ACS6) encoding 1-aminocyclopropane-1-carboxylic acid (ACC) synthas e which is an important regulatory enzyme in the ethylene biosynthetic path way. Northern analysis showed that ACS6 was induced by touch in the leaves of 3-week old light-grown plants within 5 min and reached maximum transcrip tion at 15 min. ACC, which is the product of ACC synthase and the immediate precursor to ethylene, exhibited a dramatic rise between 15 and 30 min aft er touch stimulation. Experiments with multiple touch treatments showed tha t a saturation in gene expression was obtained with one touch treatment and subsequent touch stimulations were progressively less effective in promoti ng ACS6 expression. Additional characterization of ACS6 gene expression ind icated that the gene is also induced by wounding, and by treatment with LiC l, NaCl, CuCl2, auxin, cycloheximide (CHX), aminooxyacetic acid (AOA) and e thylene. ACC levels were also increased in response to each of these treatm ents with the exception of CHX and AOA which resulted in a decrease and no effect, respectively. Our results show that ACS6 is rapidly turned on in re sponse to touch which is followed by an increase in ACC which is the immedi ate precursor to ethylene, thereby providing evidence that it is responsibl e for touch-inducible ethylene production in light-grown Arabidopsis plants . The identification and characterization of ACS6 now provides us with a to ol to better understand the involvement of ethylene produced in response to external stimuli as well as during plant growth and development.