|Calla Zalles, Bernarda|
Submitted to: Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2013
Publication Date: 4/10/2014
Publication URL: http://handle.nal.usda.gov/10113/60213
Citation: Calla Zalles, B., Blahut-Beatty, L., Koziol, L., Zhang, Y., Neece, D.J., Carbajulca, D., Garcia, A., Simmonds, D.H., Clough, S.J. 2014. Genomic evaluation of oxalate-degrading transgenic soybean in response to Sclerotinia sclerotiorum infection. Molecular Plant Pathology. 15(6):563-575. DOI:10.1111/mpp.12115. Interpretive Summary: Commercial soybean planted throughout the world are susceptible to the pathogen Sclerotinia sclerotiorum. No true resistance has been identified, only various degrees of partial resistance. A key factor to this pathogen's success is that it produces a chemical called oxalic acid that pre-conditions the plant tissue to infection. Without oxalic acid, S. sclerotiorum is a very weak pathogen. We created transgenic soybean plants that produce an enzyme found in many grasses, oxalate oxidase, that will degrade oxalic acid. We found that transgenic soybean plants expressing oxalate oxidase are resistant to this pathogen and many defense-related genes are induced more robustly in the transgenic plants. More specifically, the genes that showed the greatest difference in expression pattern between the oxlate oxidase transgenic and its non-transgenic parent were related to photosynthesis and oxidative stress, implicating an oxidative stress within chloroplasts of susceptible plants. This research will be of interest to all scientists interested in plant resistance to pathogens and in the mechanisms of that resistance.
Technical Abstract: Oxalate oxidases catalyze the degradation of oxalic acid (OA). Highly resistant transgenic soybean carrying an oxalate oxidase (OxO) gene and its susceptible parent soybean line, AC Colibri, were tested for genome-wide gene expression in response to the necrotrophic, OA producing pathogen Sclerotinia sclerotiorum using soybean cDNA microarrays. The genes with changed expression at statistically significant levels (overall F-Test p-value cutoff of 0.0001) were classified into functional categories and pathways, and were analyzed to evaluate the differences in transcriptome profiles. Although many genes and pathways were found similarly activated or repressed in both genotypes after inoculation with S. sclerotiorum, the OxO genotype displayed a measurably faster induction of basal defense responses as observed by the differential changes of defense related and secondary metabolite genes compared to its susceptible parent AC. Additionally, the experiment presented provides data on several other transcripts that support the hypothesis that S. sclerotiorum at least partially elicits the hypersensitive response, induces lignin synthesis (cinnamoyl CoA reductase) and elicits not-yet-studied signaling pathways (G protein coupled receptor and related). Of the nine genes showing the most extreme opposite directions of expression between genotypes, eight of them were related to photosynthesis and/or oxidation, highlighting the importance of redox in control of this pathogen.