Characterization and expression of four proline-rich cell wall protein genes in Arabidopsis encoding two distinct subsets of multiple domain proteins

We have characterized the molecular organization and expression of four pro line-rich protein genes from Arabidopsis (AtPRPs). These genes predict two classes of cell wall proteins based on DNA sequence identity, repetitive mo tifs, and domain organization. AtPRP1 and AtPRP3 encode proteins containing an N-terminal PRP-like domain followed by a C-terminal domain that is bias ed toward P, T, Y, and K. AtPRP2 and AtPRP3 represent a second, novel group of PRP genes that encode two-domain proteins containing a nonrepetitive N- terminal domain followed by a PRP-like region rich in P, V, K, and C. North ern hybridization analysis indicated that AtPRP1 and AtPRP3 are exclusively expressed in roots, while transcripts encoding AtPRP2 and AtPRP4 were most abundant in aerial organs of the plant. Histochemical analyses of promoter /beta-glucuronidase fusions localized AtPRP3 expression to regions of the r oot containing root hairs. AtPRP2 and AtPRP4 expression was detected in exp anding leaves, stems, flowers, and siliques. In addition, AtPRP4 expression was detected in stipules and during the early stages of lateral root forma tion. These studies support a model for involvement of PRPs in specifying c ell-type-specific wall structures, and provide the basis for a genetic appr oach to dissect the function of PRPs during growth and development.