The IRE gene encodes a protein kinase homologue and modulates root hair growth in Arabidopsis

We identified an Arabidopsis mutant, incomplete root hair elongation (ire ), whose root hairs are about 40% shorter than the wild type owing to the early cessation of their growth. In contrast, the hy5 mutant has root hairs about twice as long as the wild type, possibly because of delayed cessation of growth. Thus IRE and HY5 are likely to modify the duration of growth of root hairs. We cloned the IRE locus using the T-DNA tagged line. The IRE locus encodes a protein that includes a serine/threonine protein kinase domain. The primary structure of this kinase domain shows significant similarity to a group of protein kinases among various eukaryotes. In the Arabidopsis genome there are at least three genes that are closely related to IRE . The IRE transcript was detected in every organ examined. However, the IRE promoter-GUS fusion gene was strongly expressed in the elongating root hair cells, suggesting the cell-autonomous function of IRE in root hairs. GUS activity was also detected in pollen grains, which develop by tip growth, suggesting that IRE has a common role in the tip growth of plant cells.