EXPRESSION OF THE RICE OSGRP1 PROMOTER-GUS REPORTER GENE IS SPECIFICALLY ASSOCIATED WITH CELL ELONGATION EXPANSION AND DIFFERENTIATION

To study the expression and regulation of a rice glycine-rich cell wal l protein gene, Osgrp1, transgenic rice plants were regenerated that c ontain the Osgrp1 promoter or its 5' deletions fused with the bacteria l beta-glucuronidase (GUS) reporter gene. We report here a detailed hi stochemical analysis of the Osgrp1-Gus expression patterns in transgen ic rice plants. In roots of transgenic rice plants, GUS expression was specifically located in cell elongation and differentiation regions, and no GUS expression was detectable in the apical meristem and the ma ture region. In shoots, GUS activity was expressed only in young leave s or in the growing basal parts of developing leaves, and little GUS a ctivity was expressed in mature leaves or mature parts of developing l eaves. In shoot apices, GUS activity was detected only in those leaf c ells which were starting to expand and differentiate, and GUS expressi on was not detected in the apical meristem and the young meristematic leaf primordia. GUS activity was highly expressed in the young stem ti ssue, particularly in the developing vascular bundles and epidermis. T hus, the expression of the Osgrp1 gene is closely associated with cell elongation/expansion during the post-mitotic cell differentiation pro cess. The Osgrp1-Gus gene was also expressed in response to wounding a nd down-regulated by water-stress conditions in the elongation region of roots. Promoter deletion analysis indicates that both positive and negative mechanisms are involved in regulating the specific expression patterns. We propose a simple model for the developmental regulation of the Osgrp1 gene expression.