Transcriptomics assisted proteomic analysis of Nicotiana occidentalis infected by Candidatus Phytoplasma mali strain AT.

Phytoplasmas are pathogenic bacteria within the class of Mollicutes, which are associated with more than 1000 plant diseases. In this study, we applied quantitative mass spectrometry to analyse affected pathways of the model plant tobacco (Nicotiana occidentalis) upon Candidatus Phytoplasma mali strain AT infection. Using tissue obtained from leaf midribs, 1466 plant-assigned proteins were identified. For 1019 of these proteins, we could reproducibly quantify the expression changes of infected versus noninfected plants, of which 157 proteins were up- and 173 proteins were downregulated. Differential expression took place in a number of pathways, among others strong downregulation of porphyrin and chlorophyll metabolism and upregulation of alpha-linolenic acid metabolism, which was consistent with observed increased levels of jasmonic acid, a key signal molecule of plant defence. Our data shed light on the molecular networks that are involved in defence of plants against phytoplasma infection and provide a resource for further studies.