Characterisation of CaaX-prenyltransferases in Catharanthus roseus: relationships with the expression of genes involved in the early stages of monoterpenoid biosynthetic pathway

Abstract

CaaX-prenyltransferases (CaaX-PTases), including protein farnesyltransferase (PFT) and type I protein geranylgeranyltransferase (PGGT-I), catalyse a post-translational prenylation of proteins. In Catharanthus roseus dedifferentiated cell culture, both CaaX-PTase activities are required for the expression of genes involved in monoterpenoid biosynthesis, including the first two genes of the 2- C-methyl-erythritol 4-phosphate (MEP) pathway, Crdxs and Crdxr. In this work, we investigated the possibility that this functional relationship is also necessary in differentiated tissues. In planta, the organ-specific distribution of Crdxs transcripts was correlated with the presence of the transcripts of the β-subunit of PFT ( Crftb), PGGT-I ( Crggt_ Ib) and of the common α-subunit ( Crfta/ ggt_ Ia). Furthermore, in plant organs, Crdxs expression follows the pattern of CaaX-PTases activities. In young leaves, Crftb and Crdxs transcripts were localised to the same vascular bundles albeit in the external conducting phloem (ecp) and in the internal phloem parenchyma (ipp), respectively. Although Crftb transcripts were not detected in ipp, low transcript abundance in this tissue might hinder its detection. Alternatively, the possibility that farnesylated proteins, or other intermediates, required for Crdxs expression might translocate from ecp to ipp is discussed. Finally, we showed using prenyltransferase inhibitor that protein prenylation is also essential for the proper expression of MEP pathway genes in hairy roots.