Discovery of Myc factors: towards a green technology to improve crop yields

Scientists from INRA, CNRS and Université Paul Sabatier have determined the structure and biological activity of molecular signals called Myc factors. These compounds are synthesised by symbiotic mycorrhizal fungi. They are active at very low concentrations and can favour the growth of plant root systems and the formation of mycorrhiza, symbiotic associations of a fungus with plant roots. Processes to synthesise these compounds have been developed and will enable study of their effects on crops in order to try and improve yield without additional applications of fertilisers. These results have been published in NATURE(1) and are also the subject of a patent.

Some soil micro-organisms are able to associate with plant roots to form symbioses, some of which play very important ecological and agronomic roles. Thus arbuscular mycorrhizal symbiosis, which results from an association with fungi of the Glomales order, allows plants to improve their water and mineral nutrition, particularly that of phosphate. This is a very ancient type of symbiosis (more than 400 million years old) which seems to have accompanied the colonisation of land by plants, and it concerns more than 80% of plant species.

By studying the molecular interactions at the heart of these symbioses, the scientists have discovered symbiotic signals, or Myc factors, that are synthesised by the fungal partner. They have determined the structure of these molecular signals; they are lipochito-oligosaccharides (LCOs) which belong to the same chemical family as other symbiotic signals, the Nod factors synthesised by rhizobia which are nitrogen-fixing bacteria that live in association with legumes.

The researchers have shown that Myc factors are symbiotic signals that can stimulate the formation of mycorrhiza, in both a legume such as Medicago trunculata and in species belonging to other plant families such as marigolds (Asteraceae) and carrots (Apiaceae). Myc factors are also growth regulators that can enhance root system growth. These results were obtained under laboratory conditions. Efficient processes for the synthesis of these substances by bacteria have been developed, and will enable testing of their biological activity at a larger scale under agronomic conditions. A green technology using the treatment of seeds with other LCOs, "Nod factors", is already used to improve the yields of legumes such as soybean, alfalfa and pea on more than three million hectares[2]. It can be hoped that Myc factors will have a much broader spectrum of action and may concern the majority of cultivated plants. Thanks to the increased development of root systems, the effects anticipated from using Myc factors include, notably, improved drought resistance and an optimum exploitation of soil resources (phosphate, minerals). The aim is to be able to use these natural and biodegradable compounds to ensure improvements in the yields of numerous crops, including cereals, without additional fertilisation.

A patent has been filed to cover these findings.

Test used in the lab to study the effect of Myc factors on the root development of Medicago truncatula. On the right, in the presence of Myc factors, greater root development can be observed.

Discovery of "Myc factors": towards a green technology to improve crop yields (original article).

The article was first published on 6 January 2011.

© F. Maillet, INRA, F. Maillet