REGULATORY ELEMENTS IN-VIVO IN THE PROMOTER OF THE ABSCISIC-ACID RESPONSIVE GENE RAB17 FROM MAIZE

The rab17 gene from maize is transcribed in late embryonic development and is responsive to abscisic acid and water stress in embryo and veg etative tissues. In vivo foot-printing and transient transformation of rab17 were performed in embryos and vegetative tissues to characteriz e the cis-elements involved in regulation of the gene. By in vivo foot printing, protein binding was observed to nine elements in the promote r, which correspond to five putative ABREs (abscisic acid responsive e lements) and four other sequences. The footprints indicated that disti nct proteins interact with these elements in the two developmental sta ges. In transient transformation, six of the elements were important f or high level expression of the rab17 promoter in embryos, whereas onl y three elements were important in leaves. The cis-acting sequences ca n be divided in embryo-specific, ABA-specific and leaf-specific elemen ts on the basis of protein binding and the ability to confer expressio n of rab17. We found one positive, new element, called GRA, with the s equence CACTGGCCGCCC. This element was important for transcription in leaves but not in embryos. Two other non-ABBE elements that stimulated transcription from the rab17 promoter resemble previously described a bscisic acid and drought-inducible elements. There were differences in protein binding and function of the five ABREs in the rab17 promoter. The possible reasons for these differences are discussed. The in vivo data obtained suggest that an embryo-specific pathway regulates trans cription of the rab genes during development, whereas another pathway is responsible for induction in response to ABA and drought in vegetat ive tissues.