Gene expression profiling of Macrophomina phaseolina infected Medicago truncatula roots reveals a role for auxin in plant tolerance against the charcoal rot pathogen

Abstract

The soil-borne necrotrophic fungal pathogen Macrophomina phaseolina causes charcoal rot disease in a wide range of plant species. There are no effective control methods for this disease and no genetic resistance for M. phaseolina has been identified in most field crops. Currently, little is known about the molecular mechanisms involved in host susceptibility and resistance to M. phaseolina. Using Medicago truncatula as a model, we analyzed the global gene expression profile of M. truncatula roots infected by M. phaseolina. MAPMAN analyses identified genes involved in jasmonic acid and ethylene pathways, which are important for plant resistance against necrotrophs. In addition, genes involved in auxin homeostasis, polar auxin transport and auxin signalling were also regulated by the infection process. The differential expression patterns of these auxin-related genes suggested that the host susceptibility maybe partly due to the suppression of auxin response in the host by M. phaseolina. In additional, M. truncatula plants treated with exogenous auxin gained partial resistance against M. phaseolina, further suggesting the potential role for auxin in plant defense against this necrotrophic pathogen.