Arabidopsis Root Architecture in Response to Nitrate Supply

Modifying root system architecture (RSA) is one of the strategies aimed at developing plants that capture nutrients more efficiently, which are suited for sustainable farming with less fertilizer inputs. Our focus is on nitrate since it is the major nutritional determinant of root morphology, and because of its agronomic significance in determining yield and seed set. Learning about mechanisms of lateral roots (LRs) growth stimulation or repression by nitrate availability will help to draw strategies to modify RSA. Low nitrate levels in the soil stimulate LR development, which substantially increases the root surface area available for acquisition. Conversely, homogeneous high levels of nitrate inhibit LR elongation. We are trying to gain better knowledge about these nitrate-dependent changes in root morphology of Arabidopsis thaliana. Forward genetic dissections (mutant screens) and genome-wide association mapping are currently used to identify key genes that determine RSA. (i) By observing RSA of plants grown vertically on agar plates, it was discriminated between low nitrate mutants, those defective in LRs formation at low concentration and high nitrate mutants, those with a higher number of LRs than wt at high concentration. We have shown that chitinase-like 1 (CTL1) protein is a cross point in the regulation of several signal transduction pathways for root development under different environmental cues [1,2]. (ii) Arabidopsis has a broad geographical distribution and consequently is subject to varying environments (e.g. contrasted N availability in soils) which makes it a useful model for studying adaptation to the environment and selection. We are proceeding to a GWA mapping to identify genetic associations between marker haplotypes and the variation for biomass allocation to the root and RSA traits in >200 accessions. Our applied ambition is to transfer the benefits from Arabidopsis research to Brassica crops. Comparative genomics through a model-to-crop pipeline will allow identified key genes to be studied in crop systems.

[1] Hermans et al. (2010) Plant Physiology 152: 904-917, [2] Hermans et al. (2011) Plant Physiology 157 In press.