ARABIDOPSIS PROFILINS ARE FUNCTIONALLY SIMILAR TO YEAST PROFILINS - IDENTIFICATION OF A VASCULAR BUNDLE-SPECIFIC PROFILIN AND A POLLEN-SPECIFIC PROFILIN

Four members of the Arabidopsis profilin (pfn) multigene family have b een cloned, sequenced and analyzed. By RNA gel blot analysis it has be en shown that these four genes fall into two groups: one group (pfn1 a nd pfn2) is expressed in all organs of the plant and the other group ( pfn3 and pfn4) in floral tissues only. Based on amino acid sequence al ignment Arabidopsis profilins can be divided into the same two groups: PFN1 and PFN2 are 89% identical and PFN3 and PFN4 are 91% identical. Between these two groups they are 71-75% identical. The Arabidopsis pr ofilins bind poly-L-proline and can complement both the Saccharomyces cerevisiae profilin deletion mutant and the Schizosaccharomyces pombe cdc3-124/profilin mutation, showing that the plant profilins are funct ionally similar to yeast profilins despite the low amino acid sequence homology. Analysis of pfn promoter-GUS fusion genes in transgenic Ara bidopsis shows that pfn2 is specifically expressed in the vascular bun dles of roots, hypocotyls, cotyledons, leaves, sepals, petals, stamen filaments and stalks of developing seeds, whereas expression of pfn4 i s restricted to mature and germinating pollen grains.