Expression of defense-related genes in response to mechanical wounding and Phytophthora parasitica infection in Poncirus trifoliata and Citrus sunki

Phytophthora parasitica have caused severe damage in Citrus nurseries and orchards worldwide. The purpose of these experiments was to determine how plant defense pathways are induced by P. parasitica and if induction differs in susceptible (Citrus sunki) and resistant (Poncirus trifoliata) interactions. Furthermore, to test the effect of simple wounding on the induction of defense-related genes, plants were mechanically wounded and were monitored over the period. We monitored three categories of defense-related genes by reverse transcription real-time quantitative PCR (RT-qPCR), at 24, 48, 96, and 168 h after inoculation. The genes included pathogenesis-related, PR1 (function unknown), PR2 (β1-3 endoglucanase), PR3 (chitinase class I) and PR5 (Thaumatin-like protein); phenylpropanoid pathway such as CHS (chalcone synthase) and PAL (phenylalanine ammonia-lyase) that are involved in phytoalexin biosynthesis; and genes involved in defense and stress related categories, such as LOX (lipoxygenases) and POX (peroxidase). In accordance with the results of transcriptome changes during pathogen attack, we can suggest that all of genes are involved with resistance of the P. trifoliata to P parasitica, since the expression of these genes were significantly higher in the resistant than in susceptible genotype. Some genes were uniquely induced by pathogen (PR2, PAL and POX); or induced by the overlap involved in the response to pathogen attack and wound (PR1, PR3, PR5 and LOX); and the CHS gene was uniquely induced by wounding. This results will greatly contribute to improvement of plant resistance by genetic breeding and genetic manipulation. These genes serve as good candidates for functional studies.

► Changes occurred in P. trifoliata metabolism in response to P. parasitica infection.
► We monitored three categories of defense-related genes.
► There is a correlation between the degree of defense and genes expression level.
► The genes are related with physical barriers creation or antimicrobial properties.
► Our results will contribute to citrus breeding or genetic manipulation.