Expression of AtPRP3, a proline-rich structural cell wall protein from arabidopsis, is regulated by cell-type-specific developmental pathways involved in root hair formation

The tightly regulated expression patterns of structural cell wall proteins in several plant species indicate that they play a crucial role in determin ing the extracellular matrix structure for specific cell types. We demonstr ate that AtPRP3, a proline-rich cell wall protein in Arabidopsis, is expres sed in root-hair-bearing epidermal cells at the root/shoot junction and wit hin the root differentiation zone of light-grown seedlings. Several lines o f evidence support a direct relationship between AtPRP3 expression and root hair development. AtPRP3/beta-glucuronidase (GUS) expression increased in roots of transgenic seedlings treated with either 1-aminocyclopropane-1 -ca rboxylic acid (ACC) or alpha-naphthaleneacetic acid (alpha-NAA), compounds known to promote root hair formation. In the presence of 1 -alpha-(2-aminoe thoxyvinyl)glycine (AVC), an inhibitor of ethylene biosynthesis, AtPRP3/GUS expression was strongly reduced, but could be rescued by co-addition of AC C or alpha-NAA to the growth medium. In addition, AtPRP3/GUS activity was e nhanced in ttg and g/2 mutant backgrounds that exhibit ectopic root hairs, but was reduced in rhd6 and 35S-R root-hair-less mutant seedlings. These re sults indicate that AtPRP3 is regulated by developmental pathways involved in root hair formation, and are consistent with AtPRP3's contributing to ce ll wall structure in Arabidopsis root hairs.