Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/7/2011
Publication Date: 4/11/2011
Citation: Wisniewski, M.E., Liu, J., Cohen, L., Droby, S., Hershkovitz, V. 2011. Transcriptome analysis of grapefruit flavedo in response to application of the yeast biocontrol agent Metschnikowia fructicola [abstract]. International Congress Postharvest Pathology, Lleida, Spain, p. 38. Interpretive Summary:
Technical Abstract: Yeasts used to control postharvest pathogens have been shown to induce several biochemical defense responses in surface wounds of fruit. The capability to elicit these responses in fruit tissue has been regarded as one of the possible mechanisms of action by which yeast biocontrol agent inhibit the development of decay. To gain a better understanding of the molecular changes taking place in fruit tissue following the application of the yeast biocontrol agent, Metschnikowia fructicola, microarray analysis was performed on grapefruit (Citrus paradisi, cv Star Ruby) surface wounds using an Affimetrix Citrus GeneChip. Using a 1.5 fold change difference as biologically significant, the data indicated that 1016 putative unigenes showed significant expression changes following wounding and yeast application compared to wounded controls. These changes included a range of defense-related oxidative, signalling and secondary metabolism genes. Microarray results of select genes were validated by reverse transcription-quantitative real-time PCR (RT-qPCR). The data indicated that yeast application induced expression of Respiratory burst oxidase homolog (Rboh), two signaling mitogen-activated protein kinases (MAPK), genes encoding G-proteins, chitinase (CHI), phenylalanine ammonia-lyase (PAL) and 4-coumarate-CoA ligase (4CL). In contrast, three genes encoding a peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) were down regulated in grapefruit peel tissue treated with the yeast cells. Moreover, suppression was correlated with significantly higher levels of hydrogen peroxide, superoxide anion and hydroxyl radical production in yeast-treated surface wounds. Interestingly, high amounts of H2O2 were detected inside yeast cells recovered from wounded fruit tissue, indicating the ability of the yeast to actively produce ROS when it is in contact with plant tissue. This study provides the first global picture of gene expression changes in grapefruit in response to the yeast antagonist M. fructicola. It also provides evidence for the involvement of the yeast, M. fructicola, in regulating oxidative stress responses in wounded fruit tissue. Concomitantly, the yeast-induced oxidative burst may to the development of resistance against pathogen attack via activation of signaling pathway/s involving increased production of PR proteins and various secondary metabolites.