Blushing plants reveal when fungi are growing in their roots, a new study suggests.

Researchers have created plants whose cells and tissues blush with beetroot pigments when they are colonised by the organisms that help them take up nutrients from the soil.

This is the first time this 400 million-year-old process has been visualised in real time in full root systems of living plants, according to the experts.

Understanding the dynamics of plant colonisation by fungi could help to make food production more sustainable in the future, researchers say.

Almost all crop plants form associations with a particular type of fungi in the soil, which greatly expands their root surface area.

We can now follow how the relationship between the fungi and plant root develops, in real-time, from the moment they come into contact

This boosts the plant’s ability to take up nutrients that are vital for growth.

In a study published in the journal PLOS Biology, researchers used the bright red pigments of beetroot – called betalains – to visually track soil fungi as they colonised plant roots in a living plant.

Dr Sebastian Schornack, a researcher at the University of Cambridge’s Sainsbury Laboratory and joint senior author of the paper, said: “We can now follow how the relationship between the fungi and plant root develops, in real-time, from the moment they come into contact.

“We previously had no idea about what happened because there was no way to visualise it in a living plant without the use of elaborate microscopy.”

Researchers engineered two model plant species – a legume and a tobacco plant – so that they would produce the highly visible betalain pigments when the fungi were present in their roots.

This involved combining the control regions of two genes activated by the fungi with genes that synthesise red-coloured betalain pigments.

The plants were then grown in a transparent structure so the roots were visible, and images of the roots could be taken without disturbing the plants.

While other methods exist to visualise this process, but these involve digging up and killing the plant, and the use of chemicals or expensive microscopy.

Dr Sam Brockington, a researcher in the University of Cambridge’s Department of Plant Sciences, and joint senior author of the paper, said: “This is an exciting new tool to visualise this, and other, important plant processes.

“Beetroot pigments are a distinctive colour, so they’re very easy to see. They also have the advantage of being natural plant pigments, so they are well tolerated by plants.”

The scientists say the technique provides the ability to track and trace the presence of symbiotic fungi in soils from different sources and locations.

This will enable the selection of fungi that colonise plants fastest and provide the biggest benefits in agricultural scenarios.

The research was funded by the Biotechnology and Biological Sciences Research Council, Gatsby Charitable Foundation, Royal Society, and Natural Environment Research Council.