Mechanically Stimulated TCH3 Gene Expression in Arabidopsis Involves Protein Phosphorylation and EIN6 Downstream of Calcium

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Abstract
Mechanical signals are important both as environmental and endogenous developmental cues in plants. Among the quickest measurable responses to mechanical stimulation (MS) in plants is the up-regulation of specific genes, including TCH3, in Arabidopsis. Little is known about the signaling events and components that link perception of mechanical signals to gene expression in plants. Calcium has been identified previously as being potentially involved, and a role for ethylene has also been suggested. Using the protein kinase inhibitor staurosporine, we determined that MS up-regulation ofTCH3 expression requires protein kinase activity in young Arabidopsis seedlings. Our data from studies on the Arabidopsisein6 mutant demonstrate that the EIN6 protein is also required, but that its role in mechanically induced TCH3expression appears to be independent of ethylene. Challenge of seedlings with protein phosphatase inhibitors calyculin A and okadaic acid stimulated TCH3 expression even in the absence of MS, implying protein phosphatase activity acting to negatively regulateTCH3 gene expression. This phosphatase activity acts either downstream or independently of EIN6. EIN6 and protein kinase activity, on the other hand, operate downstream of calcium to mediate mechanically stimulated TCH3 expression.