Abstract EN:

Post-translational modification of enzyme activity is a well known ubiquitous process. In plants, reverible phosphorylations control many metabolic pathways in responses to light, phytopathogen attacks and changes of environmental factors : temperature, plant growth regulators, nutrients. . . Both phosphorylations and déphosphorylations are supposed to regulate some steps of the very complex secondary metabolic pathways of plants, leading to the biosynthesis of various compounds, many of them of pharmacological interests. The laboratory currently studies the indole alkaloids production is cultured cell suspensions (C2OD line) of periwinkle (catharansus roseus). A cDNA encoding a cytosolic cylophilin (a peptidyl prolyl cis-trans isomerase with chaperone activity) has been previously characterized. Its transcripts were found to be up-regulated in cells grown under alkaloid accumulating conditions. In the present work we investigated whether or not, the molecular partner of cyclophilin in fungal and animal cells, ie the calcium/calmoduline dependent serine/threonine phosphoprotein phosphatase (also called calcineurin or PP2B) is also present in higher plants. Indeed, in spite of several biochemical evidences of its activity, no plant equivalent of the mammal, insect or fungi calcineurin genes have been characterized to date. Based on very high similarities between the PP2BS cDNAs cloned so far, we attempted to amplify a fragment of the periwinkle gene using PCR and related methods. No calcineurin cDNA could be found in the genome of periwinkle. Similar results were obtained in other labs. , either by similar methods or by complementation of yeast calcineurin-deficien mutants with plant cDNAs. So the occurance of a plant calcineurin seems to be doubtful in plants. We also searched for cDNAs encoding other serine/threonine phosphoprotein phosphatase. We report on the amplification of two cDNAs encoding type 1 (CrPPIA) and 2A (CrPP2AI) serine/threonine phosphatase (PP1 et PP2A). We tried to determine the number of corresponding genes, and started to study their expression, both in plant organs and in C20D cell suspensions, in response to different treatments. Both the PP1 and PP2A genes are expressed in the plant, mainly in stems and flowers, but very poorly in roots and leaves. No regulation could be detected in C20D cells in response to the plant growth regulators 2,4-D, zeating and methyl jasmonate. During this work, we characterized a clone (CrABC1) encoding a part of an ABC transporter, which is similar to the Spirodella polyrrhiza TUR2 and the Saccharomyces cerevisiae PDR5 (pleiotropic drug resistance) ABC transporters. The corresponding gene is highly up-modulated by cytokinins (CKs), but is not regulated by abscissic acid. These results strongly contrast with those obtained in S. Polyrrhiza, where TUR2 is activated by ABA and downregulated by CKs. In periwinkle plants, the CrABC1 transporter seems to be mainly expressed in flowers.