THE ARABIDOPSIS PROFILIN GENE FAMILY - EVIDENCE FOR AN ANCIENT SPLIT BETWEEN CONSTITUTIVE AND POLLEN-SPECIFIC PROFILIN GENES

Profilin is a ubiquitous eukaryotic protein that regulates the actin c ytoskeleton and recently has been identified as a potent allergen in p ollen. We examined the profilin gene family in the model plant, Arabid opsis thaliana, and found that it contained approximately 8 to 10 memb ers. Four distinct profilin sequences, three cDNAs, PRF1, PRF2, and PR F3, and two genomic clones, PRF1 and PRF4, were isolated and character ized. These genes encoded four distinct profilin isoforms of 131 to 13 4 amino acids. Northern and reverse-transcriptase polymerase chain rea ction analyses demonstrated that Arabidopsis PRF1 was expressed in all major plant organs, whereas PRF4 was specifically expressed in mature pollen. Gene trees constructed from amino acid sequence data revealed the presence of two ancient, distinct profilin gene classes in plants . PRF4 was in a class with previously identified pollen-specific profi lins from monocot and dicot species. PRF1, PRF2, PRF3, and a distant d icot sequence formed a separate novel class, suggesting an ancient sep aration of plant profilins based on regulation and perhaps function. T he coevolution of plant actin and profilin classes with similar patter ns of expression is discussed. The similarity of plant, fungal, protis t, insect, and nematode profilins and their extreme divergence from th e vertebrate profilins has striking implications for the evolution of fungal-spore- and plant-pollen-profilins as allergens.