A plant protein vital to chemical signalling between plants and fungi has been discovered, revealing more about the communication processes underlying symbiosis – the mutually beneficial relationship between plants and fungi.
“This is the first plant protein ever reported to be indispensable for communication between plants and the fungus in the rhizosphere,” says study principal investigator and research group leader Dr Uta Paszkowski.
“Symbiosis starts when the plant roots and fungi exchange various types of chemical signal in the soil. Even before the two organisms have made physical contact, signalling molecules are released into the rhizosphere – the region of soil accessible to both fungus and plant root. They form symbiosis for life, so it’s an important decision.”
“Wild type plants release something that conditions the fungus for symbiosis, but if the plant can’t talk to the fungus due to the missing transporter, the fungus won’t be able to respond.”
Symbiosis significantly enhances a plant’s ability to take up vital nutrients like phosphate from the soil, and understanding the processes involved holds great promise for the development of sustainable ‘biosolutions’ to enhance food production.
By analysing a mutant strain of maize (called Zmnope1) that does not form symbiotic associations with fungi, the scientists managed to identify the missing gene – NOPE1 – which codes for a transporter molecule not previously described in plants.
The new study, published in Nature Plants, suggests that the plant’s NOPE1 gene must be working properly if beneficial fungi in the soil – called arbuscular mycorrhizal (AM) fungi – are to properly respond to signals released by plant roots and begin the process of forming this vital symbiotic relationship.
The NOPE1 gene codes for a transporter of a molecule called N-acetylglucosamine (GlcNAc), a building block of chitin, which is a major component of the cell walls of most fungi and also of many signalling molecules.
It has previously been shown in the fungal pathogen Candida albicans that when GlcNAc is transported into a fungal cell it activates cell signalling. It increases the expression of genes that promote hyphal growth leading to pathogenic interactions with a host plant. In this new study, exposure of AM fungi to the exudate of rice plant roots with functional NOPE1 had a similar effect, causing the fungi to invade the roots of plants, and also to express virulence genes that help them attach to host plant cells.
The Cambridge team’s work now provides the first evidence that the previously unknown plant GlcNAc transporter protein also plays a role at the other side of this relationship – in the initiation of plant root colonization by AM fungi.
Wild type rice roots were shown to acquire and release GlcNAc, with uptake clearly dependent on NOPE1. The transporter they identified is the first plasma membrane transporter of GlcNAc ever identified in plants.