Nucleotide Sequence of a Transcript Encoding a Germin-Like Protein That Is Present in Salt-Stressed Barley (Hordeum vulgare L.) Roots

Salt stress alters the synthesis (in vivo labeling with [35S]Met of a large number of polypeptides in roots of CM72, a relatively salt-tolerant barley (Hordeum vulgare L.) cultivar (Hurkman and Tanaka, 1987; Hurkman et al., 1989). The most significant changes are related to the biosynthesis of three polypeptides related to germin, an approximately 130kD homopentameric protein comprised of subunits of about 26 kD (McCubbin et al., 1987) that arises in the embryos of wheat seeds during germination (Grzelczak and Lane, 1984). Two 26-kD (pI 6.3 and 6.5) polypeptides accumulate and one 27-kD (pI 5.6) polypeptide declines (quantitatively in stained gels) during salt stress (Hurkman et al., 1991). NH2-terminal amino acid sequences in the 26-kD polypeptides share strong residue identity with NH2-terminal amino acid sequences in wheat germin (Hurkman et al., 1991). In addition, antisera against the barley 26-kD polypeptides react with wheat germin 26-kD polypeptides and antiserum against wheat germin reacts with the 27-kD barley polypeptide (Hurkman et al., 1991). Like wheat germin (aikaran et al., 1990), the barley 26-kD polypeptides are glycosylated (Hurkman et al., 1991), and like wheat germin oligomers (Grzelczak and Lane, 1984), the putative barley germin oligomers are protease resistant (Hurkman et al., 1988). A cDNA library constructed in Xgtl 1 using poly(A)+ RNA isolated from roots of 6-d-old CM72 seedlings grown in the presence of NaCl (Table I) was screened with a cDNA that encodes wheat germin gf-2.8 mRNA (Lane et al., 1991). A single, full-length cDNA encoding a barley germin subunit was obtained. The sequence for this barley germin cDNA is 98.5% similar to that of wheat germin gf-2.8, and it likely encodes one of the 26or 27-kD polypeptides whose levels change during salt stress. The wheat and barley germins share homology with the spherulins, putative cell-wall proteins in the slime mold Physarum polycephalum that increase during spherulation, a process brought on by environmental stresses, including osmotic stress (Lane et al., 1991). A rootspecific transcript encoding an mRNA that decreases during