A defensin gene expressed in sunflower inflorescence

Defensins are basic antimicrobial peptides that have been implicated in plant defense against microbial attack. Looking for genes that may fulfill a protective role in Helianthus annuus L. flowers, we have isolated a full length sunflower cDNA (SD2) displaying the structural features and the consensus sequence of plant defensins. The predicted protein has a signal peptide of 31 amino acids and a mature peptide of 47 amino acids with a molecular mass of 5 300 Da. The alignment of SD2 with its orthologs revealed that 21 of 47 residues are identical and another thirteen are highly conserved, thus defining a subfamily of plant defensins. Dot and northern blot analyses showed that the highest levels of SD2 transcripts are detected in flowers. SD2 gene expression is developmentally regulated during flowering, with mRNA levels increasing during flower maturation. The putative contribution of defensins to the resistance of H. annuus flowers against a fungal pathogen is discussed.