INVESTIGATION OF AN ALFALFA GENE THAT MAY BE RESPONSIBLE FOR SANCTIONING INEFFICIENT RHIZOBIA

Aims within this project includei) identifying the gene responsible for the strain-specific interaction observed betweenS. melilotiHM006 andM. sativacv. Iroquios, ii) verifying gene candidates through gain-of-function approach inM. truncatula, and iii) investigating ifM. sativacontaining the gene are able to exert a selective pressure that promotes higher populations of efficient strains in root nodules.The rhizobia competition problem has led to stagnation in research focused on enhancing nitrogen fixation in legumes through improving symbiosis. Work completed in thisproject will rekindle research into improving symbiosis with legumes by elucidating new genetics that enableM. sativato discriminate between ineffective and effective strains. The ability to discriminate between such strains may allowM. sativato maximize its own nitrogen fixation by diverting resources to more efficient strains. This affect may also lead to an active population enrichment of more effective strains inM. sativafields from year-to-year. Identifying such genes would be alandmark discoverynot only inM. sativa, but within all legumes. The genes could potentially be incorporated into other leguminous crops, further contributing to improved sustainable agriculture.The objectives for this project specifically relate to the priority area ofPlant Health and Production and Plant Products, which aims to increase "knowledge of plant systems and the various factors that affect productivity". Objectives I and II specifically aim to increase our knowledge of afactor affecting crop productivitythrough the identification of the gene responsible for ineffective symbiosis withM. sativa. Objective III specifically aims to increase our knowledge of theplant systemby investigating the extent theM. sativacontaining the gene of interest can select for and promote the population expansion of effective strains. Together, these approaches will address thecritical needto "help mitigate the ecological footprint of agriculture" as proposed by theNational Institute of Food and Agriculture (NIFA)by leading towards increased symbiotic nitrogen fixation in agricultural systems. Well-developed training activities and both collaborating mentors provide opportunities to help further my understanding of career options in both an industry and government setting.Objective I.Identifying the gene responsible for the strain-specific interaction observed between S. meliloti HM006 and M. sativacv. Iroquios.Clonally propagated plants ofM. sativacv. Iroquois that show efficient or inefficient symbiosis with HM006 enable the location of the putative sanctioning gene in theM. sativagenome through marker analysis and QTL mapping.Objective II. Verifying gene candidates through gain-of-function approach in M. truncatula.Gene candidates gathered from Objective I will be verified through a gain-of-function approach by introduction toM. truncatulaR108.Objective III. Investigating if M. sativacontaining the gene are able to exert a selective pressure that promotes higher populations of efficient strains in root nodules.Using the select-and-resequence technique, frequencies of efficient and inefficient strains will be determined when scores of rhizobial strains are inoculated on M. sativa clones that show differential symbiosis with HM006.