A noncoding plant pathogen provokes both transcriptional and posttranscriptional alterations in tomato

Viroids are single-stranded, circular, noncoding RNAs that infect plants, causing devastating diseases. In this work, we employed 2D DIGE, followed by MS identification, to analyze the response of tomato plants infected by Citrus exocortis viroid (CEVd). Among the differentially expressed proteins detected, 45 were successfully identified and classified into different functional categories. Validation results by RT-PCR allowed us to classify the proteins into two expression groups. First group included genes with changes at the transcriptional level upon CEVd infection, such as an endochitinase, a β-glucanase, and pathogenesis-related proteins, PR10 and P69G. All these defense proteins were also induced by gentisic acid, a pathogen-induced signal in compatible interactions. The second group of proteins showed no changes at the transcriptional level and included several ribosomal proteins and translation factors, such as the elongation factors 1 and 2 and the translation initiation factor 5-alpha. These results were validated by 2D Western blot, and possible PTMs caused by CEVd infection were detected. Moreover, an interaction between eukaryotic elongation factor 1 and CEVd was observed by 2D Northwestern. The present study provides new protein-related information on the mechanisms of plant resistance to pathogens.
We would like to thank the Proteomic Service of the IBMCP (Instituto de Biologia Molecular y Celular de Plantas, Valencia, Spain) for the technical assistance. We also thank Dr. Alejandro Ferrando (Instituto de Biologia Molecular y Celular de Plantas UPV-CSIC) for critical reading of the manuscript, discussions, and for kindly providing us with the eIF5A antisera. We are also grateful to Dr. Brenda Hunter (University of Arizona) for both eEF1A and eEF2 antiserum. This work was supported by Grant BFU2009-11958 from Direccion General de Programas y Transferencia de Conocimiento, from Spanish Ministry of Science and Innovation. Laura Campos was the recipient of a predoctoral fellowship ACIF/2010/231 from Generalitat Valenciana (Spain). M. Pilar Lopez-Gresa held a postdoctoral fellowship JAEDoc_08_ 00402 from the Consejo Superior de Investigaciones Cientificas (Spain).