LIGHT-REPRESSIBLE RECEPTOR PROTEIN-KINASE - A NOVEL PHOTO-REGULATED GENE FROM ARABIDOPSIS-THALIANA

To identify light-regulated genes in Arabidopsis thaliana (L.) Heynh. a clone was isolated which contains a cDNA fragment with sequence simi larity to receptor- like protein kinases (RLKs). Sequence analysis of the corresponding genomic DNA as well as determination of transcribed regions revealed that the gene comprises 12 exons. Sections of the ded uced polypeptide exhibit homologies with kinase domains and the entire protein possesses structural features indicating that it is a novel m ember of the RLK family. The protein consists of a signal peptide, a p utative receptor site including a leucine zipper region with a new mot if, a transmembrane helix and 11 subdomains characteristic of serine/t hreonine kinases. The gene is designated light-repressible receptor pr otein kinase (lrrpk), as the specific mRNA is predominantly expressed in the absence of light. The lrrpk mRNA steady-state levels were asses sed by competitive reverse transcriptase-polymerase chain reaction (RT -PCR) and found to be very low after light pulses, irrespective of the wavelength applied. Blue light was least effective in this; respect, and the repression was not reversible by far-red light. Employment of in-situ RT-PCR revealed elevated lrrpk mRNA levels in the cotyledons o f etiolated seedlings. The mRNA was also increased in the outer region s of the roots of greenhouse-grown A. thaliana, but was not detectable in any other part of the plants. An explanation of the relatively low lrrpk mRNA levels and the photophobic expression of the gene could be the finding that in the 5' upstream region of the lrrpk gene sequence elements are present that are similar to those identified in promoter s of phytochrome A genes.