Plant Defense Responses in Medicago truncatula Unveiled by Microarray Analysis

Plant defense responses are made up of broad plant defense mechanisms that involve an integrated signaling pathway. Powdery mildew caused by Erysiphe pisi is one of the most important diseases of pea. However, the mechanisms and pathways involved in the resistance against E. pisi are yet undiscovered. We studied the transcriptome of two Medicago truncatula genotypes, the powdery mildew susceptible commercial variety Parabinga and the resistant accession SA1306, at 4 and 12 h after E. pisi infection, using Mt16kOLI1 microarrays. Four hundred and forty six probes were differentially expressed between the two M. truncatula genotypes along the time points studied. RNA accumulation patterns suggest that the most prominent responses to pathogen infection occur at early infection stages. Most of the regulated genes are related to cell wall reinforcement, flavonoid, and phenylpropanoid biosynthesis. In addition, pathogenesis-related proteins and signaling pathways controlled by jasmonic acid and salicylic acid were found to be regulated during pathogen infection. This study provides the first comprehensive view of the genes and pathways activated in the E. pisi/M. truncatula pathosystem, allowing the identification of targets against this important disease.