Changes in the expression of CrFTA, the Catharanthus roseus farnesyltransferase α-subunit gene, in response to a Candidatus Liberibacter asiaticus infection

The farnesyltransferase α-subunit (FTA) may be involved in the regulation of defence responses against pathogens in plants. In this study, this gene was amplified from Catharanthus roseus (CrFTA gene). The cDNA was found to be 1 403 bp long, and encodes a putative protein of 331 amino acids that contains a conserved PPTA motif. The phylogenetic analysis showed that the sequence of CrFTA is the most similar to that from Coffea canephora. The qRT-PCR assays indicated that CrFTA is expressed in the leaves, stems, and roots. During a Candidatus Liberibacter asiaticus (Ca. L. asiaticus) infection, the CrFTA expression levels significantly increased and reached 18-fold that measured in the control group, after which its expression decreased gradually from 22 days after top-grafting (DAT) to the end of the experiment. Spray application of Manumycin A (ManuA), a specific inhibitor of farnesyltransferase, on the leaves of C. roseus plants caused a significant decrease in the CrFTA expression and a significant increase in the Ca. L. asiaticus positivity percentage after top-grafting with the Ca. L. asiaticus-infected shoots compared with the groups not treated with ManuA. Furthermore, ABA had no significant effect on the relative expression of CrFTA and the number of Ca. L. asiaticus-positive plants. These results suggest that CrFTA most likely plays a role in mediating the tolerance to a Ca. L. asiaticus infection in C. roseus.