Characterisation of sunflower-21 (SF21) genes expressed in pollen and pistil of Senecio squalidus (Asteraceae) and their relationship with other members of the SF21 gene family

Two related flower-expressed gene copies belonging to the SF21 (sunflower-21) gene family have been isolated from Senecio squalidus (Oxford Ragwort, Asteraceae). These gene copies are differentially expressed in pollen and pistil tissues; ORSF21B (Oxford Ragwort SF21B) is expressed exclusively in mature pollen, whereas ORSF21A (Oxford Ragwort SF21A) is expressed in the transmitting tissue of the style, where it is developmentally regulated. Despite differences in expression, the coding regions of ORSF21A and ORSF21B are highly similar. Amino acid sequence alignments of SF21 genes from a number of angiosperm species indicate that this gene family is conserved in flowering plants and may play an important role in reproductive processes in a wide range of taxa. Phylogenetic analysis of SF21 nucleotide sequence alignments supports this theory, and indicates a complicated history of evolution of this gene family in angiosperms. The putative roles of SF21 genes in reproduction and pollen-pistil interactions are discussed.