Team:Purdue/Description

     Rice is a calorie-dense staple crop central to the diets of half the globe. Its relative ease of cultivation, multiple harvests per year, and cultural importance for the majority of humanity makes rice critical to feeding our growing population. However, 30 percent of rice crops are damaged worldwide by Magnaporthe oryzae, commonly known as rice blast fungus (Watkinson, Boddy & Money, 2015). The rice lost due to M. oryzae alone could feed 60 million people globally, and U.S. rice producers suffer $70 million in economic losses annually due to M. oryzae infection (Nalley, Tsiboe, Durand-Morat, Shew & Toma, 2016). The ability of rice blast fungus to infect crops can be partially attributed to its ability to bypass the plant's innate immune response. Rice plants have receptors that are able to detect fungal chitin and trigger the subsequent defense mechanisms that would inhibit the spread of the fungal infection. However, M. oryzae secretes a chitinase to break down any chitin before it can be detected by the rice plants (Yang et al., 2019). This can have a significant effect on rice yields, one study even found that “some yield losses associated with rice blast outbreaks have reached 50% or more emphasizing the need for a solution” (Nalley et al., 2016).
     Prior solutions to combat the disease focus on modifying various resistance genes in rice to increase the immune response against the fungus. A major limitation of these solutions is their strain-specific design. One particular solution researched by the University of Delaware focused on the chemical signals released by M. oryzae that suppress plant immunity. The chemical signal identified and targeted was recognized not only by rice plants and other plants, like wheat, susceptible to the disease. Inspired by this approach, we decided to stimulate rice’s innate immunity to fight against M. oryzae.
     Purdue iGEM is developing a method of preemptively stimulating an antifungal immune response in rice to effectively inhibit M. oryzae infection of rice crops. In order to accomplish this, we will introduce NodC, a chitin synthase homolog, into Pseudomonas fluorescens, a bacterium that naturally lives on rice leaves (Debelle, Rosenberg & Denarie, 1992). The introduction of this chitin synthase into P. fluorescens will produce excess chitin that will be secreted out of the cell and recognized by the plant. Chitin oligomers are pathogen-associated molecular patterns (PAMPs) that bind to pattern recognition receptors on the surface of the rice plant, which subsequently induces the expression of an immune response that inhibits fungal growth (Yang et al., 2019). The secreted chitin would, therefore, result in PAMP-triggered immunity against M. oryzae in rice plants exposed to the modified P. fluorescens.
     References
  1. Debelle, F., Rosenberg, C., & Denarie, J. (1992). The Rhizobium, Bradyrhizobium, and Azorhizobium NodC proteins are homologous to yeast chitin synthases. Molecular Plant Microbe Interactions, 5, 443-443.
  2. Marcel, S., Sawers, R., Oakeley, E., Angliker, H., & Paszkowski, U. (2010). Tissue-adapted invasion strategies of the rice blast fungus Magnaporthe oryzae. The Plant Cell, 22(9), 3177-3187.
  3. Nalley, L., Tsiboe, F., Durand-Morat, A., Shew, A., & Thoma, G. (2016). Economic and environmental impact of rice blast pathogen (Magnaporthe oryzae) alleviation in the United States. PloS one, 11(12), e0167295.
  4. Shahbandeh, M. (2019, May 8). Total global rice consumption 2019. Retrieved from https://www.statista.com/statistics/255977/total-global-rice-consumption/
  5. Watkinson, Sarah & Boddy, L & Money, N.P.. (2015). The Fungi: Third Edition.
  6. Yang, C., Yu, Y., Huang, J., Meng, F., Pang, J., Zhao, Q., ... & Liu, J. (2019). Binding of the Magnaporthe oryzae chitinase MoChia1 by a rice tetratricopeptide repeat protein allows free chitin to trigger immune responses. The Plant Cell, 31(1), 172-188.