Arabidopsis transcription factors, RAV1 and RAV2, are regulated by touch-related stimuli in a dose-dependent and biphasic manner

Transcription factors, RAV1 and RAV2 from Arabidopsis thaliana, contain two distinct DNA-binding domains, AP2/EREBP and B3, both of which are uniquely found in plants. We found that transcripts of RAV1 and RAV2 were upregulated transiently by touch-related mechanical stimuli. However, the temporal expression patterns of RAV1 and RAV2 differed from those of known touch-induced genes. A striking feature of mechanical stimulus-induced expression of RAV1 and RAV2 was that it was biphasic; the RAV1 and RAV2 expression was reinduced and sustained after a rapid and transient induction. The extent of both transient and subsequent upregulation by touch-stimuli depended on the dose of the initial stimulus. Analysis of transgenic A. thallana plants carrying a RAV2 promoter-GUS fusion gene indicated that the transient mechanical stimulus-induced RAV2 expression was primarily controlled by its promoter. Histochemical analysis of the transgenic plants revealed that GUS expression was strongly induced in the petioles and primordia of true leaves and shoot apical. meristems, which may be related to the alteration in plant growth pattern caused by touch-stimuli. Because RAV1 has been suggested to be a negative regulator of growth and development, the dose-dependent biphasic upregulation of RAV1 and RAV2 may serve not only for immediate physiological responses and but also for developmental adaptation in response to the environmental stimuli.