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Getting to the root of nutrient sensing

 

A new research supported by Agropolis Fondation reveals a mechanism that enables plants to modify their root architecture based on nutrient availability in the soil. The study, published by Cell Press in the June 15th issue of the journal Developmental Cell, provides support for an original mechanism of nutrient sensing in higher organisms.

Terrestrial organisms like plants obtain necessary nutrients by transporting them out of the soil through their roots. Plants cannot easily move to a new environment when conditions are less than favorable, but they can modify their roots in response to soil conditions. Therefore, they must have some mechanism for perceiving the availability of external nutrients, like nitrogen, and eliciting an appropriate adaptive response.

Studies with Arabidopsis, an excellent model organism for studying plant biology, have shown that nitrate rich soil induces lateral root growth. "Nitrate is the main nitrogen source for these plants and a signal molecule that regulates growth and metabolism," explains senior study author Dr. Alain Gojon from the Integrative Biology Institute for Plants in Montpellier, France. "In Arabidopsis, the NRT1.1 nitrate transporter is crucial for nitrate signaling governing root growth. However, although it has been proposed to act as a nitrate sensor, the sensing mechanism is unknown."

The researchers found that in addition to transporting nitrate, the NRT1.1 transporter also facilitated auxin uptake. When external nitrate concentrations were low, NRT1.1 repressed auxin accumulation in lateral roots and lateral root growth. The researchers went on to show that disruption of NRT1.1 enhanced auxin accumulation in lateral roots and the growth of these roots at low, but not high nitrate concentration.

Taken together, the results indicate that NRT1.1 regulated root branching by exerting nitrate-dependent control of auxin accumulation in lateral roots. "We propose that NRT1.1 represses lateral root growth at low nitrate availability by promoting auxin transport out of lateral root tips and towards the base of the root and promotes lateral root growth at high nitrate concentrations by inhibiting auxin transport and allowing auxin accumulation in root tips," says Dr. Gojon. "This defines a mechanism connecting nutrient and hormone signaling during organ development."

The project was supported by Agropolis Fondation (07024) under its first call for proposals and welcomed a post-doc student: Francine Perrine-Walker.