Plant genes required for arbuscular mycorrhiza symbiosis

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The phosphate acquiring arbuscular mycorrhiza (AM) symbiosis between plant roots and Glomeromycota fungi is of prime ecological importance and bears potential for sustainable agriculture. We would like to unravel the molecular mechanisms that control development and regulation in this symbiosis. To this end, we have initiated a genetic screen for AM-defective individuals within an ethylmethane sulfonate (EMS)-mutagenized population of the model legume Lotus japonicus. This approach has resulted in a collection of 21 mutants that exhibit defects at various stages of AM development while maintaining the capacity to form root nodules. These mutants provide a valuable tool to dissect the plant's contribution to symbiosis. We propose a detailed characterization of the genes involved in AM both at the phenotypic and molecular level. For this we will describe the mutant phenotype by microscopy, transcriptional profiling and analysis of AM performance. We will continue the genetic characterization of the mutants by defining rough map positions and complementation groups. At least two of the mutants display defects at early developmental stages, and twelve mutants are impaired during arbuscule development. We propose to identify at least two of the defective genes by map-based cloning. Subsequently, we will functionally characterize the identified genes and their gene products. So far, not a single gene specifically required for AM symbiosis has been identified through forward genetic approaches. The results from this study will therefore provide novel and important insights into the genetic basis of AM.