Genetics of the Nod-independent legume Aeschynomene evenia to shed light on the evolution of rhizobial symbioses and to engineer nitrogen fixation in crop plants – AeschyNod

The tropical Aeschynomene legumes use a unique Nod-independent infection process that is believed to correspond to an ancestral state of the nitrogen-fixing rhizobium-legume symbiosis. The study of this system should therefore shed new light on the origin and evolution of symbiosis by uncovering the basic underlying the process of nodulation.
However, the interest of such symbiotic system is just emerging and knowledge of Aeschynomene genetics and genomics is still limited. To bypass these limitations, the Laboratoire des Symbioses Tropicales et Méditerranéennes (UMR LSTM) has recently identified A. evenia as an ideal species to constitute a bona fide model legume and developed tools for functional approaches.
To permit the identification of the molecular determinants controlling the Nod-independent process, we propose here the project “AeschyNod” (Aeschynomene Nodulation). This aims at performing a “mutagenesis” strategy to generate and screen plant mutants defective for nodulation. To make successful this strategy, we will also make use of the Next-Generation Sequencing (NGS) technologies to develop a draft genome sequence of A. evenia. The availability of a dense genetic map anchored to genomic sequence data will accelerate the map-based cloning of symbiotic genes.
The acquired knowledge, thanks to the comparative genomic analysis with conventional legumes and the identification of nodulation genes using the plant mutants, will bring important highlights on the specificity of the Nod-independent process and on the evolution of the nitrogen-fixing symbiosis in the legume family.
It may also be used to improve or engineer nitrogen fixation in crop plants, both in related legumes such as arachid, which belongs to the same basal Dalbergioid as Aeschynomene, and non-legumes, in particular cereals for which the demand in nitrogen is very high. Promoting nitrogen-fixing symbiosis represents a key issue for tomorrow’s agriculture that needs to comply with a growing demand in a more sustainable and ecological way.