No abstract

A nove1 hydroxyproline-rich glycoprotein (SbHRGP3) that consists of two different domains is encoded by an extensin gene from soybean. The first domain (domain 1) located at the N terminus is composed of 11 repeats of Ser-Pro4-LysHis-Ser-Pro4-Tyr3-His, whereas the second domain (domain 2) at the C terminus contains five repeats of Ser-Pro4-Val-TyrLys-Tyr-Lys-Ser-Pro4-Tyr-L~~r-Pro-Ser-P~~-~yr-Lys-Tyr-Pro-Ser-Pro4-Val-~r-Lys-Tyr-L~. These two repeat motifs are organized in an edremely well-odered pattern in each domain, which suggests that SbHRGPB belongs to a new group of proteins having the repeat motlfs of two distlnct groups of dicot extensins. The expression of the SbHRGP3 gene increased with seedling maturation, and its expression was relatively hlgh in the mature regions of the hypocotyl and in the root of soybean seedlings. An SbHRGP3-p-glucuronidase (SbHRGP3-GUS) chimeric gene was constructed and expressed in transgenlc tobacco plants. The expression of the SbHRGP3-GUS gene was not induced by wounding alone in transgenlc tobacco plants; sucmse was also required. Expression was specific to phloem tissues and cambium cells of leaves and stems. In transgenic tobacco seedllngs, SbHRGP3-GUS gene expression was activated by the maturation of the primary root and then inactivated; however, reactivation was specifically at the epidermis of the zone from which the lateral root was to be initiated. Its reactivation occurred just before the lateral root initiation. These results indicate that the SbHRGP3 gene in different tissues responds to different signals.

A novel extensin gene has been identified in soybean (Glycine max L.) that encodes a hydroxyproline-rich glycoprotein (SbHRGP3) with two different domains. In this study expression of SbHRGP3 was investigated during soybean root development. SbHRGP was expressed in roots of mature plants, as well as seedlings, and showed a distinct pattern of expression during root development. The expression of SbHRGP3 increased gradually during root development of seedlings and reached a maximum while the secondary roots were maturing. The maximum expression level was contributed mainly by the secondary roots rather than by the primary root. Furthermore, expression of SbHRGP3 was preferentially detected in the regions undergoing maturation of the primary and secondary roots. These results imply that the expression of SbHRGP3 is regulated in an organ- and development-specific manner and that in soybean SbHRGP3 expression may be required for root maturation, presumably for the cessation of root elongation. Wounding and sucrose in combination enhanced expression of SbHRGP3 in roots, whereas both wounding and sucrose were required for the expression of SbHRGP3 in leaves.