Phosphorus and nitrogen are critical macronutrients for plant proper growth. Many fertilisers, such as phosphorus and nitrogen are applied to soil for higher crop yield in agriculture system, but only 30% applied fertilizers are taken up by crops. The remainder is either immobilized in the soil, or carried into ground water and river, often resulting in pollution. A beneficial fungus which forms relationships with plant such as maize and rice roots is effective at helping plants thrive in nutrients poor conditions, in this process which could reduce the high levels of fertilizers currently used in agriculture system. Arbuscular mycorrhizal (AM) symbiosis is one of the most widespread and ancient symbiosis on earth, which should date back to fossils (400 Mya). 

The research from the team led by WANG Ertao in Shanghai Institutes for Biological Sciences showed that the rice line mutated in DELLA are unable to be colonized by mycorrhizal fungi. DELLAs are well known, since DELLAs regulate pathway triggered by plant hormones, Gibberellins which affect many aspects of plant development. DELLAs act as a node for crosstalk in nutrient responses, abiotic stress, light perception and several interacting hormones including auxin, ethylene, abscisic acid and brassinosteroids.  

Through a series of experiments that researchers found that DELLA interacts with a second GRAS protein, DIP1 (DELLA Interacting Protein 1) which is also required for mycorrhizal colonisation and in turn interacts with a previously characterised mycorrhizal GRAS protein, RAM1, that has been shown to directly regulate mycorrhizal associated gene expression. This research revealed that a new DELLA protein complex is necessary for regulation of AM symbiosis and sheds light on how plants coordinate its growth, development and nutrients usage by symbiotic association. 

This work entitled “A DELLA protein complex controls the arbuscular mycorrhizal symbiosis in plants” has been published online in Cell Research on December 17. This work is supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA08010401). 

Mechanism of DELLA-DIP1-RAM1 protein complex in mycorrhizal symbiosis (Image by Dr. WANG Ertao's research team)