A POLLEN-SPECIFIC GENE FROM SUNFLOWER ENCODES A MEMBER OF THE LEUCINE-RICH-REPEAT PROTEIN SUPERFAMILY

A pollen-specific cDNA clone (SF17) has been isolated from a sunflower floral cDNA library, The cDNA encodes a leucine-rich protein of 540 amino acid residues with a molecular mass of 61.7 kDa. Structural features of the predicted polypeptide include an N-terminal hydrophyllic domain, a region containing blocks of leucine-rich repeat elements (LRR) and two hydrophobic transmembrane domains at the C-terminus. The LRR region of the SF17 protein contains nine imperfect tandem repeats of 24 amino acids in length, which are homologous to the leucine-rich repeats found in a variety of proteins widely distributed among eukaryotic cells, The analysis of a genomic copy encoding the SF17 protein revealed the presence of two introns. The transcription start site was determined by primer extension analysis. During pollen development SF17 mRNA was detected only in mature pollen grains indicating that the SF17 gene belongs to the class of 'late' pollen genes, Southern hybridization analysis showed that the gene exists in small copy number in the sunflower genome. The features of SF17 protein suggest that it might be involved in signal transduction events during pollen development and/or pollination.