Suppression of the ribosomal L2 gene reveals a novel mechanism for stress adaptation in soybean

Pseudomonas syringae pv, glycinea bacteria or zoospores of the fungus Phyto phthora sojae were used to trigger a hypersensitive reaction (HR) in cell c ultures of soybean (Glycine mns [L,] Merr. cv. Williams 82). During a scree n for genes that show an altered expression as a response to dying neighbou r cells we have identified a gene fragment that is specifically but transie ntly down-regulated in an HR. The corresponding cDNA codes for the ribosoma l protein L2 (rpL2) of 80S ribosomes, which is essential for the peptidyltr ansferase activity. Two gene copies of rpL2 exist in soybean and both genes are transcribed. The temporary down-regulation of the rpL2 genes is follow ed by a transient block in the synthesis of new proteins as visualised by p ulse-labelling experiments using S-35-amino acids. The same basic phenomeno n was also found after treatment of soybean cells with other stress-causing compounds such as elicitors or heavy metals. It is suggested that the tran sient block in protein synthesis allows a more rapid depletion of, fur exam ple, signal molecules with a short half-life time and thus leads to a faste r adaptation of the cellular protein inventory to the new environmental con ditions.