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Sweet Talks between Plants and MicrobesMost of our research is dedicated to beneficial associations between plants and microbes. The vast majority of land plants develop mutualistic associations with arbuscular mycorrhizal (AM) fungi that improve the plants ability to acquire nutrients, especially phosphate and nitrogen, from the soil and their resistance to biotic and abiotic stresses. Legumes also enter into a nitrogen-fixing symbiosis with soil bacteria known as rhizobia that results in the formation of root nodules. A combination of microbial genetics and biochemistry elucidated bacterial and plant factors that mediate the often-high level of host specificity observed in the rhizobia-legume symbiosis (Brelles-Mariño and Ané, 2008; Mukherjee and Ané, 2011; Venkateshwaran and Ané, 2011; Venkateshwaran et al., 2012; Delaux et al., 2013). Legume roots are exquisitely sensitive to bacterial signals named Nod factors which are necessary for nodule development and infection of plant roots. A somehow similar “molecular dialog” was recently identified in arbuscular mycorrhization with symbiotic fungi producing diffusible Myc factors. We like to refer to these signals exchanges as “sweet talks” since Nod and Myc factors are lipo-chito-oligosaccharides (LCOs).
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Evolution of symbiotic associations in land plants and beyond.We analyze the evolution of plant and microbial mechanisms identified through genetic approaches. For instance, we characterized plant symbiotic genes in soybean (Zhu et al., 2006), in rice (Zhu et al., 2006; Chen et al., 2008; Mukherjee and Ané, 2011) and even in early diverging lineages of land plants such as liverworts and hornworts (Wang et al., 2010; Delaux et al, 2013; Delaux et al., 2015 ). We also analyzed the loss of arbuscylar mycorrhizal associations in various angiosperm lineages including the Brassicales (Delaux et al., 2014).
Interestingly some of these mechanisms are found in Charophyte green algae suggesting that these Charophyte algae may engage in symbiotic associations that have not yet been identified (Knack et al., 2015). We also use comparative phylogenomic approaches to understand the critical innovations that gave rise to arbuscular mycorrhizae as well as root nodule symbioses (Delaux et al., 2014). We also analyze the similarities and differences between arbuscular mycorrhizae and ectomycorrhizae using poplar and pines as model systems (Garcia et al., 2015). |
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Practical applications of research on plant-microbe symbiosesImproving the use of bacterial and fungal inoculants in the field
Soybean growers have been inoculating their seeds with rhizobia for almost one hundred years. However, the decision to inoculate is sometimes difficult especially after events such as the floods which occurred in Wisconsin in 2008. Testing the amount of rhizobia in the soil is classically done using the Most Probable Number (MPN) technique which takes more than a month to yield results. In collaboration with Dr. Shawn Conley (UW Madison, Agronomy), we developed a high-throughput procedure based on real-time PCR to quantify soybean rhizobia in the soil in just a few days (Furseth et al., 2010). Such a tool has already proven to be valuable for both farmers and agronomists in order to determine in which conditions seed inoculation with rhizobia is necessary and cost-effective (Furseth et al., 2011; Furseth et al., 2012). The summer of 2012 was characterized by a long drought throughout the United States. We are currently testing the impact of drought on the survival of soybean rhizobia in the soil in order to help farmers in their decision to inoculate their seeds or not for the next growing season. Along the same lines, we are currently working on improving the use of mycorrhizal inoculants for organic carrot production in collaboration with Dr. Erin Silva (Plant Pathology, UW Madison) and Dr. Phillip Simon (Horticulture, UW Madison). Engineering efficient nitrogen fixation in poplar and cereals We are working on the characterization of maize accessions that can acquire 30-70% of their nitrogen from the air by hosting nitrogen-fixing bacteria in the mucilage produced by their aerial roots. This project was initially started by the Mars Inc. company and collaborators at the University of California-Davis, which led to some legal concerns. However, this N-FARM (Nitrogen-Fixation in Aerial Roots of Maize) project is now publicly funded by the USDA and based on publicly-available accessions from the CIMMYT and the USDA ARS GRIN. We are also working with Dr. Claudia Calderon, Dr. Natalia deLeon and Dr. Shawn Kaeppler on breeding this trait into accessions that can be used in the US but also in developing countries. We also found a similar trait in sorghum accessions. We are characterizing publicly-available accessions from the ICRISAT and working to introduce this trait into sorghum accession for food and biofuel production. We are also characterizing the microbial communities in this mucilage using approaches of synthetic communities and systems biology. This soNar (sorghum Nitrogen-fixation in aerial roots) project is publicly funded by the DOE. It is an exciting collaboration with Dr. Wilfred Vermerris at the University of Florida, and Dr. Ophelia Venturelli and Dr. Sushmita Roy at the University of Wisconsin-Madison. We are also working, in close collaboration with Dr. Sushmita Roy, Dr. Matias Kirst, Dr. Douglas Soltis, Dr. Pamela Soltis and Dr. Robert Guralnick on a project aiming at engineering nitrogen-fixing symbioses between rhizobia and non-leguminous crops (poplar and cereals). This Nit_Fix project is funded by the DOE. These projects could transform the ways in which the nitrogen nutrition of food and biofuel crops are met and reduce the dependence of our agriculture on nitrogen fertilizers. |
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