ROOT-SPECIFIC EXPRESSION OF A GLYCINE-RICH PROTEIN GENE IN BRASSICA-NAPUS

We have constructed complementary DNA and genomic libraries from Brass ica napus and isolated clones corresponding to three closely related s equences encoding glycine-rich proteins. A probe from BnRG22, the most expressed sequence in 7-day old seedlings, identified a major transcr iption signal at 1.2-kb, highly abundant in roots and detected also in stems but not in other organs of the plant. The synthesis of these tr anscripts is regulated during development up to 30 days after germinat ion. Moreover, flooding and drought have antagonistic effects on its e xpression. BnRG22 encodes a protein containing as much as 62% of glyci ne residues and an amino-terminal signal peptide. This protein shows t hree repeats of 42 residues each and includes the (Gly-X)(n) and many Gly-Tyr-Gly motifs. We propose for this protein a structural model fea turing a beta-pleated sheet domain made of anti-parallel strands.