No abstract

Stress response at the protein level to viral infection in orchid plants has not been extensively investigated to date. To understand the proteomic basis of Phalaenopsis amabilis's responses to Cymbidium Mosaic virus (CymMV), and/or Odontoglossum ring spot virus (ORSV), the total proteins were extracted from Phalaenopsis amabilis leaves infected with CymMV, ORSV, or both respectively. Differentially expressed proteins were identified by two-dimensional electrophoresis, and 27 of these proteins that had significant changes were further examined by mass spectrometry. Comparing CymMV-infected leaves with mock-inoculated ones, 2 proteins were significantly up-regulated, 9 were significantly down-regulated and 1 previously undetected protein was identified. 10 proteins were significantly up-regulated, 3 significantly down-regulated and 1 previously undetected protein was identified in ORSV-infected leaves. 6 proteins were significantly up-regulated and 9 significantly down-regulated proteins were found in co-infected leaves. These identified proteins are involved in disease resistance, stress response, transcriptional regulation, energy metabolism, protein modification and the previously unknown proteins were not involved with known protein pathways. Proteins significantly up-regulated were ATP sulfurylase, down-regulated proteins included glutamate decarboxylase isozyme 2, RNA polymerase alpha subunit and chloroplastic peptide deformylase 1A were proteins with similar alteration trend after all infection treatments. Significantly up-regulated were Thioredoxin H-type and down-regulated Cytosolic phosphoglycerate kinase I which were proteins that have been shown to be specifically regulated by the infection with CymMV. Significantly up-regulated were proteins like Rubisco large subunit, Triosephosphate isomerase, NADP-specific isocitrate dehydrogenase and Cinnamoyl CoA reductase CCR2 by the infection of ORSV. Protein regulation in coinfected leaves followed a pattern similar to that of any of the single virus infection results. These experiments demonstrated that an exogenous pathogen infection in plants, regardless of viral type or pattern, induced a protein defense response system and a number of metabolism changes in P. amabilis with detectable protein alterations. These cellular alterations appeared to be specific responses to different pathogens. We suggest that altered proteins above might play important roles in pathogenesis and metabolic interactions between P. amabilis and viruses that infect them.