Extracellular calmodulin accelerates rbcS-GUS expression in suspension-cultured transgenic tobacco cell

The role of extracellular calmodulin in regulating expression of rbcS in da rkness was examined. A suspension-cultured cell line was generated from the transgenic rbcS-GUS tobacco. It was demonstrated that purified calmodulin added to the media enhanced rbcS-GUS expression. The time course of express ion of rbcS-GUS and that of the secretion of calmodulin in the suspended tr ansgenic tobacco cells in darkness were very similar. Both showed initial i ncrease followed by decline with maximum calmodulin secretion preceding max imum GUS expression. The addition of membrane-impermeable calmodulin antago nist W7-agarose inhibited the expression of rbcS-GUS in darkness, but this inhibitory effect was completely reversed by adding exogenous purified calm odulin. These results provide the first evidence that extracellular calmodu lin accelerates rbcS gene expression.