A flower-specific gene family whose expression is regulated temporally and spatially during flower development in sunflower

One genomic (SF15G) and four different cDNA clones (SF15-49, SF15-2, SF15-3 and SF15-45) expressed in the young green closed sunflower (Helianthus annuus L.) inflorescence were isolated and characterized. Northern blot analysis revealed temporal regulation of the sf15 gene family: the transcripts accumulate transiently between stage 1 and 4 of Boret development and disappear before the florets reach maturity. The SF15 mRNAs were undetectable in male-sterile sunflower plants. In situ hybridization experiments showed that expression of the SF15 transcripts occurs in the anther epidermal cell layer as well as in immature pollen, in the corollar tissue, and in the papillar cells of the stigma. The sf15 gene encodes a putative polypeptide of 280 amino acids with a molecular weight of 31.7 kDa. The Eve sunflower SF15 proteins are highly homologous to each other (82-99% nucleotide and amino acid sequence identity). They are basic (isoelectric point of 9.6) and have a potential N-terminal signal peptide, indicating that they may enter the secretory pathway. The presence of a short hydrophobic C-terminal domain in the protein encoded by the genomic sequence but not in the proteins encoded by the cDNAs suggests an extracellular as well as a vacuolar location for this family of proteins. Southern blot analysis shows that in sunflower the sf15 gene exists as a family of genes with approximately six to eight family members. The sf15 gene is also present in the maize, tomato and cabbage genomes.