Proteomic Analysis in Arabidopsis thaliana inoculated with a beneficial endophytic Streptomyces sp. in response to a challenge by the pathogen Fusarium oxysporum

Two-dimensional difference gel electrophoresis (DIGE) was used to elucidate the changes occurring in the Arabidopsis leaf proteome in response to interactions with the beneficial endophyte Streptomyces sp. EN27 (Str. sp. EN27); the hemibiotrophic wilt pathogen, Fusarium oxysporum (Fox); as well as the threeway interaction between endophyte, pathogen and plant. Of the 1440 protein spots that were matched across all gels, a total of 28 spots significantly changed in abundance due to the various treatments, with the plant responding similarly to the endophyte and pathogen. Eight spots were identified by LC MS/MS and grouped into functions of defense-related, cell redox, and metabolism. Expression of genes encoding the identified proteins as well as genes typically involved in the defense response, such as PDF1.2, PR-1 and Hel that were not identified in the DIGE analysis was analysed by quantitative PCR (qPCR), which revealed poor correlation between transcript and protein levels. qPCR analysis of the
defense transcripts showed that plant defense against Fox employed salicylic acid (SA) and jasmonic acid (JA) pathways by upregulation of PR-1 and PDF1.2, respectively. In contrast Str. sp. EN27-mediated defense resulted in increased expression of LLP and Hel. Str. sp. EN27 also appeared to strongly suppress JA signalling, known to facilitate pathogen-mediated leaf chlorosis and senescence. This may may explain the lack of wilt symptoms and survival of the Str. sp. EN27-treated plants seven days post-inoculation with Fox.