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

We have constructed complementary DNA and genomic libraries from Brassica napus and isolated clones corresponding to three closely related sequences encoding glycine-rich proteins. A probe from BnRG22, the most expressed sequence in 7-day old seedlings, identified a major transcription 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 transcripts is regulated during development up to 30 days after germination. Moreover, flooding and drought have antagonistic effects on its expression. BnRG22 encodes a protein containing as much as 62% of glycine residues and an amino-terminal signal peptide. This protein shows three 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 featuring a beta-pleated sheet domain made of anti-parallel strands.