Department of Life Sciences and Systems Biology

Project description

Chito-oligosaccharides treatment Implementation to Reinforce Crop LEgume Symbioses (CIRCLES)

In both natural and agricultural ecosystems, legumes develop two beneficial symbioses with soil microbes: arbuscular mycorrhizas (AM) with glomeromycete fungi and symbiotic nitrogen fixation (SNF) with rhizobiacean bacteria. AM fungi play key nutritional functions: through their hyphal network, AM host plants gain preferential access to soil water, phosphorus (P) and nitrogen (N). SNF implies the formation of a novel organ, the root nodule, a host-controlled niche for N-fixation. Atmospheric N2 fixation to NH3 allows a significant reduction in the use of N fertilizers, with positive consequences on soil and air pollution. Although both AM fungi and rhizobia are normally present in agricultural soils, plant symbiotic aptitudes have not always been favored by breeders. This dual symbiotic aptitude raises great interest in staple crops such as soybean for the sustainability of agroecosystems and food security strategies in line with the EU green deal program, allowing a major and environment-friendly reduction in fertilizer input.

Field application of Nod factors - rhizobial signaling molecules – has proven very effective in promoting nodulation. AM symbiosis has so far been more recalcitrant to manipulation, but recently, Myc factors (AM counterparts to Nod factors) and their receptors have been characterized. Lipo-chito-oligosaccharides (LCOs) and tetra/pentameric chito-oligosaccharides (COs) were shown to be released in AM fungal exudates and activate host symbiotic signaling. Furthermore, COs were active in all tested AM hosts, depicting short-chain COs as universal Myc factors and paving the way to possible applications in agriculture.

Plant treatment with COs at sowing, with watering or by spray, induces a robust and reproducible increase in AM colonization and plant biomass under both laboratory and field conditions. Preliminary observations from field samples suggest that CO treatment may also enhance legume nodulation. Since fact Nod factors are LCOs, i.e. COs decorated with different functional groups, rhizobia might use exogenous COs as substrates for Nod factor biosynthesis, thereby reinforcing their symbiotic signaling. In addition, a shared common symbiotic signaling pathway (CSSP) regulates both AM and SNF establishment and the CO over-activation of CSSP might therefore reinforce signaling -and hence root colonization- by both symbionts.

Chito-tetraose, a bioactive Myc-factor

Results and publications

WORKPACKAGES

Line 1 – Balance of AM and SNF under CO treatment
- effect of CO treatment on SNF and AM establishment
- CO-dependent gene regulation contributing to AM and SNF

Line 2 – Effect of CO treatment on plant signaling
- Ca²⁺ signals in root plastids
- strigolactone production
- potential interplay of plastids and endoplasmic reticulum during symbiotic signalling

Line 3 - Cross talk between CO signaling, nutrient availability and transport
- effects of CO on AM and SNF based on plant nutritional status
- role of symbiotic nitrate and phosphate transporters 

Line 4 – Soybean treatments
- Tests on Glycine max 
- Phenotyping at Phenolab platform