STRUCTURE AND REGULATION OF TOBACCO EXTENSIN

A tobacco cDNA clone (pCNT1) was characterized that encodes an extensi n apoprotein almost entirely composed of the repeats Ser-Pro4(-Lys2), Pro-Tyr2-Pro2-His and Thr-Pro-Val-Tyr-Lys. In healthy plants extensin transcripts are abundant in the roots, less prevalent in the stem and rare in the leaves. In leaves extensin mRNA is induced by wounding, et hylene or virus infection. Tobacco was transformed with pCNT1 cDNA cou pled in sense or antisense orientation to the CaMV 35S promoter. Analy sis of transgenic plants that over- or underexpressed pCNT1 mRNA demon strated that the encoded protein constituted the majority of hydroxypr oline-rich glycoproteins in roots, stems and leaves. The pCNT1-encoded protein contained at least 50% of total hydroxyproline present in the se organs and was abundant in the soluble protein fraction of stems an d roots as well as in the cell wall of stem vascular bundles. Analysis of transgenic plants expressing sense or antisense extensin gene cons tructs showed no correlation between total hydroxyproline concentratio n or soluble HRGP content and plant development.