Objectifs scientifiques et projet de recherche

To feed the population that is growing exponentially, it is necessary to increase crop yield while maintaining soil health and fertility. Legume is a kind of staple food that serves for people all over the world. Some of legumes were used as a green manure to fertilize the soil and improve the physical, chemical, and biological soil properties. Leguminous plants including soybean (Glycine max ) and peanut (Arachis hypogaea ) were also used to produce oil, feed, and as ingredient in many food industry and pharmaceutical industry. As well as for genus Vigna that is one of legumes that have been used directly as food, such as adzuki bean (V. angularis), the black gram (V. mungo), the cowpea (V. unguiculata ), and the mung bean (V. radiata ), which is used as a whole bean, a bean paste, or as bean sprouts. Fortunately, these legumes do not require large amounts of chemical fertilizers for their cultivation because they are able to develop a symbiotic interaction with nitrogen-fixing bacteria, called rhizobia. These rhizobia can be used as biofertilizer to support plant growth and yield. The most important cultivated tropical legumes, such as A. hypogeae , G. max, and Vigna sp. are nodulated by Bradyrhizobium strains. To select the best strain to be used as biofertilizer, the factor of plant host compatibility and the efficiency of nitrogen fixation should be considered. The LSTM and the PMBP Thai team (Plant-Microbe interaction and Biofertilizer production research unit) work since several years on the nitrogen-fixing symbiosis between tropical legumes and Bradyrhizobium strains. Our laboratories have collaborative projects under the Franco-Thai Cooperation Programme in Higher Education and Research, BEST, and ARTS projects.
The previous collaborative projects were focused on the functional study of nodulation (nod) and nitrogen fixation (nif) genes of an indigenous Bradyrhizobium strain of Thailand, DOA9, which can be developed as a broad host range biofertilizer for several tropical legumes. The LSTM provided the knowledge on the construction of genetic tools and training of young scientists for performing the research on molecular genetics of plant-microbe interactions, which are very useful for strengthen the scientific research skill of PMBP team. This collaborative research has provided a recent breakthrough in the field of the plant-bacteria interactions by showing an alternative symbiotic process based on the used by the bacteria of a Type 3 secretion system (T3SS), a weapon normally used by pathogenic bacteria to infect plant and animal host. The T3SS machinery permits the delivery of effector molecules inside the host cells where they suppress defense responses and favor the infection. Our work revealed that T3SS effector(s) can also directly activate the plant nodulation signaling pathway in the absence of the conventional bacterial signal, the Nod factors. In addition, we have obtained recent data showing that the T3SS of our model Bradyrhizobium strains can drastically impact, positively or negatively, their ability to interact symbiotically with several tropical legumes of agronomical importance. Since the genome sequence of these strains is available, we propose to investigate the role of T3SS effectors on various cultivated legumes, in particular different species of Vigna plant, which several breeding lines are available in Thailand. This research will permit to elucidate the common effectors that play an important role in inhibition or promotion of legume-rhizobium symbiosis. This project will help to strengthen the collaboration between our two teams and in the same time encourage young scientists to the higher level of research.
This knowledge from this project will be of great help to develop a sustainable agriculture in the South countries with the improving of legume-rhizobium symbiosis efficiency and the way to improve broad host range biofertilizer.

Unités IRD

4R04000 : LSTM

Partenaires / Unités de recherche associés

SUT : Suranaree University of Technology

Responsable

Mme. Panlada TITTABUTR

Correspondants

M. Eric GIRAUD

Disciplines scientifiques

Sciences de la Terre, univers, espace

Thématique(s)

- To perform a basic research on the understanding of the molecular basis of the symbiosis between Bradyrhizobium strains and tropical legumes.
- To perform an applied research by identifying the T3SS effectors that modulate the plant defense immune response and act positively on the symbiotic interaction with economic Vigna plants. The understanding on how the T3SS effectors govern legume-rhizobia compatibility could permit the selection of efficient symbiotic couples and/or permit the engineering of inoculum strain as biofertilizer.
- To fulfill the advanced research skills in plant-microbe interactions and strengthen the research network between French and Thai partners through the exchange of young scientists from both sides.
Altogether, this work will deepen our understanding of the role of the T3SS in rhizobial interaction with legumes and this new obtained knowledge is expected to be usable for the development of strategies for a sustainable agriculture.