Nitrate sensing and signaling in plants

► Nitrate in not only a major nutrient for the plant but also a signal molecule. ► Plants are able to sense nitrate in their environment. ► Nitrate is sensed by transceptors that activate several signaling cascades. ► Nitrate availability modulates expression of up to 10% of the genome. ► Nitrate modulates plant growth and development in a nutrition independent manner. ► Several key molecular actors (transcription factors, kinases) have been identified. Nitrate (NO3−) is a major nutrient for plants, taken up by their roots from the soil. Plants are able to sense NO3− in their environment, allowing them to quickly respond to the dramatic fluctuations of its availability. Significant advances have been made during the recent period concerning the molecular mechanisms of NO3− sensing and signaling in the model plant Arabidopsis thaliana. The striking action of NO3− as a signal regulating genome expression has been unraveled. Note worthily, NO3− sensing systems have been identified. These correspond to membrane transporters also ensuring the uptake of NO3− into root cells, thus generalizing the nutrient ‘transceptor’ (transporter/receptor) concept defined in yeast. Furthermore, components of the downstream transduction cascades, such as transcription factors or kinases, have also been isolated. A breakthrough arising from this improved knowledge is a better understanding of the integration of NO3− and hormone signaling pathways, that explains the extraordinary developmental plasticity of plants in response to NO3−.