The Arabidopsis ACTIN-RELATED PROTEIN 2 (AtARP2) promoter directs expression in xylem precursor cells and pollen

To investigate the role of the actin cytoskeleton in plant growth and development, we have cloned and determined the DNA sequence of a gene encoding an actin-related protein (arp) from Arabidopsis thaliana (AtARP2) and studied its expression patterns. A. thaliana appears to have only one AtARP2 gene which contains 14 introns, an unusually large number when compared to 4 or 5 introns in the actin genes isolated so far. The predicted protein shows high homology to and shares typical peptide insertions with arp2 proteins from other organisms. The AtARP2 transcript is present in all plant tissues, at a very low level, and is down-regulated by light. Promoter-GUS expression studies showed that the AtARP2 promoter directs activity predominantly in a very small number of cells immediately adjacent to the xylem in all organs. In addition, strong expression was observed in pollen grains. We discuss the potential role of an arp2/3 complex in plant development.