The Arabidopsis Profilin Gene Family (Evidence for an Ancient Split between Constitutive and Pollen-Specific Profilin Genes)

Abstract

Profilin is a ubiquitous eukaryotic protein that regulates the actin cytoskeleton and recently has been identified as a potent allergen in pollen. We examined the profilin gene family i n the model plant, Arabidopsis thaliana, and found that it contained approximately 8 t o 10 members. Four distinct profilin sequences, three cDNAs, PRF1, PRFZ, and PRF3, and two genomic clones, PRFl and P R M , were isolated and characterized. These genes encoded four distinct profilin isoforms of 131 to 134 amino acids. Northern and reversetranscriptase polymerase chain reaction analyses demonstrated that Arabidopsis PRFl was expressed in all major plant organs, whereas PRF4 was specifically expressed in mature pollen. Cene trees constructed from amino acid sequence data revealed the presence of two ancient, distinct profilin gene classes i n plants. PRF4 was in a cot and dicot species. PRF1, PRFZ, PRF3, and a distant dicot sequence formed a separate nove1 class, suggesting an ancient separation of plant profilins based on regulation and perhaps function. The coevolution of plant actin and profilin classes with similar patterns of expression is discussed. l h e similarity of plant, fungal, protist, insect, and nematode profilins and their extreme divergence from the vertebrate profilins has striking implications for the evolution of fungal-spore-and plant-pollen-profilins as allergens.class with previously identified pollen-specific profilins from monoThe actin cytoskeleton of eukaryotic cells undergoes rapid and dynamic rearrangements in response to externa1 stimuli and during the cell cycle. The reorganization of the cytoskeleton is highly regulated both temporally and spatially through a wide spectrum of ABPs (Stossel et al., 1985;Pollard and Cooper, 1986;Hartwig and Kwiatkowski, 1991). These ABPs cross-link actin filaments into loose networks or tight bundles, cap the ends or block the sides of the filaments, sever the filaments, or sequester actin monomers from polymerization. Specific interactions between ABP and either monomeric or polymerized forms of actin control the three-dimensional organizations and cellular locations of the actin cytoskeleton, which in turn affects the functions of the actin cytoskeleton in the cell.

The Regulation of Actin Organization by Actin-Depolymerizing Factor in Elongating Pollen Tubes[W]

“…In particular, NtADF1 is 68% identical and 86% similar to the pollen ZmADF1, whereas these levels decrease to 58 and 79%, respectively, compared with the vegetatively expressed ZmADF3, consistent with the view that pollenexpressed genes are substantially more diverged from their vegetative counterparts (Huang et al, 1996;Meagher et al, 1999aMeagher et al, , 1999b. The deduced secondary structure of NtADF1 also shows significant homology with other ADF/cofilins.…”

Parallel up-regulation of the profilin gene family following independent domestication of diploid and allopolyploid cotton ( Gossypium )

“…Profilin is a protein of 130-134 aa encoded by a small gene family. Plant profilins fall into two classes, one thought to be constitutively expressed and the other predominantly expressed in anthers or pollen (31)(32)(33)(34). The size of the profilin gene family varies among plants.…”

Pollen Profilin Function Depends on Interaction with Proline-Rich Motifs

“…Multiple profilin isoforms could be required for tissue-specific or temporal regulation of profilin expression, as has been suggested for multiple actin genes in plants (Meagher, 1991). In fact, profilin isoforms display tissue-specific expression patterns in maize (Staiger et al, 1993) and Arabidopsis (Christensen et al, 1996;Huang et al, 1996). Multiple isoforms of profilin are expressed in the pollen of many species, which raises the question whether these are functionally redundant or whether they perform unique functions.…”

“…The positions of highly conserved residues, which are present in the majority of eukaryotic profilins, are indicated as follows: asterisk, PLP binding; (ϩ), polyphosphoinositide binding; and pound sign, actin binding (see text for details). The sequences used for the alignment, their sources, and GenBank accession numbers or original citations are as follows: ZmPRO4, Zea mays profilin 4, AF032370 (this study); ZmPRO1, maize profilin 1, X73279; ZmPRO2, maize profilin 2, X73280; ZmPRO3, maize profilin 3, X73281; BvPRO1, Betula verrucosa profilin, M65179; AtPFN1, Arabidopsis thaliana profilin 1, U43325 (see also Huang et al, 1996); AtPFN2, Arabidopsis profilin 2, U43326 (see also Huang et al, 1996); AtPRF3, Arabidopsis profilin 3 (Huang et al, 1996); AtPFN3, Arabidopsis profilin 3, U43323 (see also Huang et al, 1996); and AtPFN4, Arabidopsis profilin 4, U43324. Multiple sequence alignments were created using the PileUp program from the Genetics Computer Group (Madison, WI; Devereux et al., 1984).…”