GENE REGULATION BY TOR PATHWAY IN RICE BLAST FUNGUS (MAGNAPORTHE ORYZAE)
Associated group: Dr. Ane Sesma
Rice is the most widely distributed dietary staple in the world. It also represents a significant percentage of global farmland reaching up to 160 million hectares each year. One of the most devastating rice pathogen is the blast fungus, Magnaporthe oryzae. Yield losses caused by blast disease oscillate between 10-30 % per annum, which, even at the most conservative estimate, are sufficient to feed 60 billion people (Skamnioti&Gurr, 2009). M. oryzae is considered a hemibiotrophic fungus. Fungal metabolism plays an essential role during M. oryzae plant invasion. We are interested in identifying genes involved in the nutritional adaptation of the fungus by dissecting M. oryzae TOR signaling pathway. Given the significant role that the TOR pathway plays in the cell, the new genes identified as a result of this research line could be used as targets for developing small molecule inhibitors. The knowledge of how plant pathogens interact with important crops will ultimately provide Spanish agriculture with new sustainable strategies to maintain and improve crop production and will strength the Spanish research effort in plant pathology. Spain and Italy are the two main producers of rice in Europe and they are affected by blast disease. The development of effective and durable strategies for disease control depends on a better understanding of the disease process. This, in turn, will enhance the European ‘knowledge-based bio economy’ (a concept originally conceived in the Lisbon agenda), which is of strategic importance. Additionally, RNA metabolism and TOR pathway in the fungal kingdom has been poorly studied in filamentous fungi (more complex organisms compared to model yeasts). Thus results derived from this research will therefore not only be relevant for the scientific community working on rice blast, but for the mRNA processing community in general. This research area has a broad relevance for post-transcriptional mechanisms of gene regulation and TOR pathway in all eukaryotic cells.
Up-left a Rice field, and down-left Rice leaves infected with M.oryzae. Right, microscopy picture from a spore with an appressorium.
TOR is a conserved serine/threonine kinase present in all eukaryotes from fungi to humans. It is also a key component of the most central nutrient-sensing signal transduction pathways in eukaryotic cells. While the TOR kinases are broadly conserved, distinct strategies in utilizing the TOR signaling cascade have been developed by fungal organisms.
Rbp35 is a polyadenylation factor present only in filamentous fungi. The nutrient-dependent behaviour of the rbp35mutant, together with its accelerated autophagy and higher tolerance to rapamycin, strongly suggests that the target of rapamycin (TOR) pathway is significantly altered. In fact, TOR is the most severely affected signalling pathway in this mutant. A comparative genome-wide poly(A) site mapping analysis has identified the involvement of Rbp35 in alternative polyadenylation (APA) in M. oryzae. In carbon-depleted cells, eighteen out of the thirty components of the TOR signalling pathway are alternatively polyadenylated (APA). Based on these results, Rbp35 acts as a key modulator of the TOR pathway.
Multi-layer regulation of Rbp35 in M. oryzae. Three different transcripts are produced at the RBP35 gene locus, the RBP35 mRNA and two smaller RNAs derived from the 5’ UTR, namely, uORF1 and uORF2. The uORF1 controls M. oryzae growth activated by the TOR pathway. Translation of the mRNA generates the full-length isoform of the protein, Rbp35A. This step is regulated by its C-terminal Met-Asn-Gly do- main. Post-translational processing of Rbp35A generates a second isoform Rbp35B, which interacts with both Rbp35A and CfI25 within the fungal CfI25/Rbp35 complex. The processing site of the protein is after the RGG region. Cleavage efficiency, localization and degradation processes are regulated by the RGG domain
The aim of this research line is to dissect links between pre-mRNA 3’end processing and the TOR pathway, and how these two processes regulate the expression and function of infection-related genes in M. oryzae. Using two complementary approaches that combine classical genetics with high-throughput genomics and molecular with cellular biology, this research will reveal1) the type of genetic interactions that link Rbp35 and the TOR pathway, and 2) how Rbp35-dependent 3’UTR processing can regulate this signalling pathway.
It is well studied that TOR regulates the expression of proteins required for the adaptation to nutritional cues. Therefore, this project will identify new proteins that are relevant for the adaptation of the fungus to external environment. These experiments will also enable us to understand how the expression of genes involved in the TOR signalling pathway is being affected at post-transcriptional level. This will be achieved by looking at mRNA decay rates, subcellular localisation of mRNAs and translation rates.
Results derived from our research are relevant for food security and crop protection. This research line also has practical implications to develop durable and sustainable strategies for disease control, which directly depend on a better understanding of the disease process. We expect to gain knowledge in M. oryzaeTOR signalling pathway.Given the significant role that the TOR pathway plays in the cell, the new genes identified as a result of this research could be used as targets for developing small molecule inhibitors.
- Genetic interaction between the TOR pathway and mRNA processing in the rice blast fungus (MINECO, 2015- 2018. BIO20014-54233-JIN) PI: Julio L. Rodríguez-Romero
- Post-transcriptional networks regulating organ-specific and general infection mechanisms in the rice blast fungus. Marie Curie Reintegration grant 2012-2016 (FP7-2011-CIG). PI: Ane Sesma
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