Identification of defence-related genes expressed in coffee and citrus during infection by Xylella fastidiosa

One of the phytosanitary problems of coffee cultivation in Brazil is Coffee Leaf Scorch (CLS) disease, caused by the phytopathogenic bacterium Xylella fastidiosa. Due to the economic importance of coffee to Brazil and the losses caused by X. fastidiosa, a cDNA library (RX1) was constructed using infected coffee stems. This library is one of the 37 coffee EST libraries constructed using different organs and tissues and biological conditions (Coffee Genome Project-CafEST). The objective of this study was to identify genes potentially involved in defence processes in response to X. fastidiosa infection by in silico analysis of the transcripts from the RX1 library as well as compare the coffee ESTs to citrus Xylella-infected ESTs. Clustering analysis of the RX1 library grouped a total of 7,501 sequences into 3,248 contigs, 19 of which were not found in the other 36 libraries. Additionally, 119 contigs were considered differentially expressed in comparison with the other libraries and according to statistical criteria. The global analysis of these contigs showed several genes involved in dehydration and photosynthesis. A total of 2,235 singlets were also obtained in the RX1 library and several of these genes are classically involved in defence processes. The comparison to a Xylella-infected citrus EST library revealed several genes similarly modulated in both species, indicating common defence mechanisms in both host plants in response to X. fastidiosa. The results obtained showed that water deprivation and response to osmotic and oxidative stress were expressed in a similar way in both coffee and citrus libraries. This is the first study to propose a common mechanism shared by citrus and coffee plants in response to the same pathogen.