Expression profiling of Italian ryegrass (Lolium multiflorum Lam.) during infection with the bacterial wilt inducing pathogen Xanthomonas translucens pv. graminis

Bacterial wilt caused by Xanthomonas translucens pv. graminis (Xtg) may lead to severe damage and substantial yield losses in Italian ryegrass, Lolium multiflorum Lam. To identify candidate genes for marker-assisted breeding and to investigate the molecular basis of the host-pathogen interaction, this study focused on searching the ryegrass genome for resistance genes and key signal transduction elements in the defence response. cDNA-amplified fragment length polymorphism (AFLP) was used to analyse differentially expressed genes at six time-points after infection in a partially resistant genotype of L. multiflorum infected with Xtg. A total of 87 selective primer combinations resulted in 173 differentially expressed transcript-derived fragments (TDF) out of which 37 TDFs were isolated. Database searches revealed sequence homologies of various TDFs to sequences such as ERBP-transcription factors, an TGF-beta receptor interacting protein, a terpene synthase and various other genes expressed in response to bacterial and fungal infection. Reverse transcription-polymerase chain reaction (RT-PCR) and quantitative RT-PCR (qRT-PCR) confirmed the expression patterns found by cDNA-AFLP. The TDFs identified represent candidate genes for the identification of quantitative trait loci (QTLs) involved in resistance to bacterial wilt. These TDFs may also allow for the identification and analysis of avirulence genes expressed by Xtg. The results of this study provide a valuable basis not only for a better understanding of the genetic control of resistance to bacterial wilt in Italian ryegrass, but primarily for the development of molecular tools to improve resistance breeding.