|Norelli, John (jay) - Jay|
Submitted to: Plant Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/1/2012
Publication Date: 9/10/2012
Citation: Liu, J., Macarisin, D., Wisniewski, M.E., Sui, Y., Droby, S., Norelli, J.L., Hershkovitz, V. 2012. Production of hydrogen peroxide and expression of ROS generating genes in peach flower petals in response to host and non-host pathogens. Plant Pathology. 62:820-828. Interpretive Summary: Brown rot of stone fruits in the U.S. is caused by the fungus, Monilinia fructicola. It is the major cause of postharvest decay and infects blossoms and twigs as well. There is very little disease resistance to brown rot present in commercial cultivars or in the germplasm being used in breeding programs. Additionally, very little is known about what makes the brown rot fungus so virulent. In response to wounding and pathogen invasion, plants often exhibit an oxidative burst producing a large amount of compounds that contain highly reactive forms of oxygen, known as reactive oxygen species (ROS). ROS can play dual roles in plant-microbe interactions in that they can either stimulate host resistance or benefit the infection process. The current study examined the role of ROS in the infection process of peach petals by the brown rot fungus. The results indicate that the brown rot fungus induces a great amount of ROS production during the infection process and that this is caused by the activation of genes in the plant that code for ROS-producing enzymes. The high production of ROS led to severe tissue damage which aided the infection process. ROS production was not observed when the peach petals were inoculated with a non-compatible fungus. ROS production and the infection process could be blocked by the application of antioxidant compounds such as ascorbic, caffeic, or chlorogenic acids. The results of this study provide a better understanding of the pathogenicity of the brown rot fungus that can lead to potentially new brown rot management strategies involving the use of antioxidants. These approaches will be explored in future studies.
Technical Abstract: Reactive oxygen species (ROS) play dual roles in plant-microbe interactions in that they can either stimulate host resistance or benefit pathogen virulence. Accumulation of ROS was determined in peach petals in response to Monilinia fructicola (a compatible pathogen) and Penicillium digitatum (an incompatible pathogen). Infection by M. fructicola is facilitated by the induction of ROS in peach petals. Fluorescence microscopy was utilized to detect ROS production in peach petals. Gene expression and activity of ROS-generating enzymes, NADPH oxidase (NOX) and cell wall peroxidase (POD), were studied using reverse transcription-PCR and an enzymatic assay. Oxidative damage to protein and lipid was measured spectrophotometrically. M. fructicola induced ROS accumulation in petals, whereas P. digitatum did not. Application of exogenous antioxidants significantly reduced brown rot disease incidence and symptom. M. fructicola induced both nox and pod gene transcription and enzyme activity. Moreover, petals inoculated with M. fructicola showed high levels of protein carbonylation and lipid peroxidation. M. fructicola was shown to trigger ROS accumulation in peach, potentially by activating host nox and pod which resulted in infection.