Characterization of a cDNA encoding a putative extensin from developing barley grains (Hordeum vulgare L.)

A partial cDNA clone Hvex1 from Hordeum vulgare L. encoding a putative hydr oxyproline-rich protein of the extensin family was isolated in an experimen t designed to identify transcripts differentially expressed in the coenocyt ic endosperm and the surrounding sporophytic tissues during the early stage s of grain development. The amino acid sequence derived from the Hvex1 cDNA has a high proportion of Pro, Lys and Thr residues, and a pI of approximat ely 11. However, the deduced Hvex1 polypeptide has an unusual structure unl ike those of known monocot extensins and consists of four domains with repe ats of the sequences KPP, PKPAPPTY(K/S)P, SPPAYKPAPKV, and (H/Y)KPPTPTPPA, respectively, and a fifth domain with a single SPPPP motif. In situ hybridi zation and Northern analyses reveal that Hvex1 transcripts are expressed in the nucellus, the nucellar epidermis and the nucellar projection of develo ping barley grains. In addition to nucellar tissues, the Hvex1 transcript i s also detected in the vascular tissue of the pericarp, scutellum of the de veloping embryo, stigma, and root tips. The Hvex1 transcript is encoded by a single gene located near the centromere of barley chromosome 2.