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Seminar: "Necrotrophs possess more complex virulence strategies: evidence from the Macrophomina phaseolina-Sorghum bicolor pathosystem"

Ananda Bandara - Postdoctoral scholar, Department of Plant Pathology & Environmental Microbiology, Pennsylvania State University

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February 19, 2018, 3:35 PM - 4:30 PM

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Macrophomina phaseolina (MP) is a soil-borne, necrotrophic fungal pathogen that causes diseases in over 500 plant species. The charcoal rot disease caused by this pathogen is a great concern in many economically important crops including sorghum. However, the genetic basis of charcoal rot resistance is poorly understood. Classically, necrotrophs are thought to kill the host using various phytotoxins, reactive oxygen and nitrogen species (ROS/RNS), and cell wall degrading enzymes that are secreted into the host tissues. A genome-wide transcriptome study (RNA-seq) conducted during my graduate carrier at Kansas State University revealed that MP manipulates diverse aspects of the sorghum plant’s metabolism and plant defense responses, providing new insights into “induced host susceptibility” at a broader scale. RNA-seq data suggested MP’s capacity to up-regulate ROS/RNS synthesis and cell wall/membrane degradation in a charcoal rot susceptible sorghum genotype, Tx7000; but not in the resistant genotype, SC599. In this seminar, I will show various biochemical experiments that were conducted to functionally validate the up-regulated ROS/RNS biosynthesis and enhanced oxidative stress, and enhanced activities of host cell wall degrading enzymes such as polygalacturonase, pectin methylesterase, and cellulase in charcoal rot susceptible genotypes Tx7000 and BTx3042 after MP inoculation. Implications of the dynamics of host antioxidant system including peroxidase, glutathione S-transferase, glutathione peroxidase, and glutathione reductase on charcoal rot disease reaction will also be addressed. Further, as revealed via lipidome analysis, evidence for lethal impacts of MP inoculation on plastid- and cell- membrane integrity and the lipid-based signaling capacity of charcoal rot susceptible sorghum genotypes will be discussed. As our findings suggested, the ability of MP to induce disease susceptibility appears to be an effective virulence strategy. This might elucidate the success of MP as a pathogen with a broad host range.