A NOVEL BLUE LIGHT-INDUCIBLE AND ABSCISIC ACID-INDUCIBLE GENE OF ARABIDOPSIS-THALIANA ENCODING AN INTRINSIC MEMBRANE-PROTEIN

Continuous irradiation with blue light (400-500 nm) induces flower for mation in plantlets of Arabidopsis thaliana (C24) while red light (600 -700 nm) is ineffective. This observation started a search for genes t hat are activated by blue light and initiate the morphogenic programme leading to flower formation. Several genes were identified via their cDNAs. From these clone AthH2, with an open reading frame for a hydrop hobic 30.5 kDa polypeptide, was selected for further characterization of the corresponding gene. From a genomic library a DNA fragment of ab out 6.4 kb was isolated, comprising the coding region as well as 5'-up stream and 3'-downstream flanking segments. The coding region is compo sed of four exons, which specify a polypeptide of 286 amino acids. Sev eral potential regulatory elements were found between position - 670 a nd - 1140 including GA and ABA sequence motifs. The latter could accou nt for the observed induction of the AthH2 gene by ABA. Southern blot analysis of Arabidopsis genomic DNA suggests that the AthH2 gene is en coded by a single-copy gene. Hydropathy plots and secondary structure analysis of the putative polypeptide predict six membrane-spanning dom ains implicating a function as transmembrane channel protein. It displ ays significant homology with the proteins TR7a of pea (82%) and RD 28 of A. thaliana (68%).