Characterization of two soybean repetitive proline-rich proteins and a cognate cDNA from germinated axes.

Abstract

We have resolved and analyzed two proline-rich proteins isolated from the walls of soybean cells in culture. The proteins are similar in amino acid content, containing 20% proline, 20% hydroxyproline, 20% lysine, 16% valine, 10% tyrosine, and 10% glutamate. The proteins undergo a rearrangement or a limited cleavage in dilute NaOH, but are otherwise remarkably stable to a high concentration of alkali. We have cloned and sequenced a cDNA from soybean axes germinated for 31 hours (1A10-2) coding for a protein that closely corresponds in its amino acid content to that of the proline-rich proteins. The cDNA sequence predicts a decameric repeat of Pro-Pro-Val-TyrLys-Pro-Pro-Val-Glu-Lys. Consequently, this class of proteins is referred to as repetitive proline-rich proteins, i.e., RPRP2 and RPRP3. We have also analyzed RNA gel blots with probes that discriminate between the new cDNA clone and a related cDNA previously reported [SbPRPl;Hong, Nagao, and Key (1987). J. Biol. Chem. 262, 8367-83761. Messenger RNAs from young seedlings and from soybean suspension cultures correspond primarily to the new RPRP clone (1A10-2), whereas the predominant mRNA accumulating later in the roots corresponds to SbPRPl.

Role of the Extensin Superfamily in Primary Cell Wall Architecture

“…Finally, the diagnostic Ser-Hyp 4 peptide (Smith et al, 1986) enabled identification of the first extensin (Chen and Varner, 1985) and PRP cDNAs (Hong et al, 1987;Tierney et al, 1988;Datta et al, 1989) as bona fide proteins with the hallmark of other structural proteins, most notably collagen, which is also Hyp rich and the major structural fibrillar protein of animals. Collagen polypeptides occur in an extended poly-Pro-II lefthanded helical conformation, which was also con-firmed in carrot extensin by further circular dichroism spectra (van Holst and Varner, 1984), with evidence for the role of carbohydrate in maintaining the backbone conformation (Stafstrom and Staehelin, 1986).…”

Pipeline to Identify Hydroxyproline-Rich Glycoproteins

“…Only a single PRP was identified in soybean (Table I; Fig. 4), one of the few species in which non-chimeric PRP gene sequences have been reported (Datta et al, 1989). The previously cloned SbPRP1 (Glyma09g12198.1), SbPRP2 (Glyma09g12252.1; Fig.…”

“…The extent of glycosylation of PRPs remains unclear, as it has not been studied extensively. For example, purified soybean (Glycine max) PRPs were shown to be minimally glycosylated, constituting less than 3% carbohydrate, with Ara residues presumably linked to Hyp (Datta et al, 1989;Fig. 1).…”

Ultrastructural Localization of a Bean Glycine-Rich Protein in Unlignified Primary Walls of Protoxylem Cells.

“…The promoter of a tobacco HRGP expressed a reporter gene only at sites of lateral root initiation, indicating that this particular HRGP is involved in strengthening the cell walls at the tip of the emerging lateral root . Besides HRGPs (reviewed by Cassab and Varner, 1988), plant cell walls contain proline-rich (Datta et al, 1989;Hong et al, 1989) and glycine-rich (Condit and Meagher, 1986;Keller et al, 1988;Condit et al, 1990) proteins. Genes encoding glycine-rich proteins (GRPs) were also described in rice (Lei and Wu, 1991), barley (Rohde et al, 1990), tomato (Showalter et al, 1991), and Arabidopsis (de Oliveiraet al, 1990).…”