Plant roots are the primary mechanism for absorbing water and nutrients from the soil. Breeding for deeper and more branched root systems would enhance the extractive properties of roots. This involves first identifying key genes and proteins responsible for optimal root phenotypes, and subsequently altering their expression in order to determine the roles of regulatory elements in root development. By manipulating rice root architecture, we aim to maximize water and nutrient use efficiency in high-intensity, modern agricultural systems.
Two rice varieties with contrasting root architecture phenotypes - a lowland rice with shallow roots (IR64) and an upland rice with deeper roots (Azucena) - were grown under control and water deficit conditions. In order to focus of the development of new root tissues, three sections distal to the root apex were sampled: 0 – 5 mm (Z1), 5 – 10 mm (Z2) and 10 – 15 mm (Z3); three variables were therefore analysed - genotypes, water supply and developmental zones. Quantitative proteomic analysis using TMT labelling identified and quantified 7,509 proteins from Azucena and 8,011 proteins from IR64. Differentially abundant proteins were calculated from normalized TMT label peak area intensities. Hierarchical clustering and heat maps showed that the proteomics profiles of Z1 samples clustered together irrespective of genotype and conditions, and were highly distinctive compared with Z2 and Z3, which clustered closely together.
Proteins associated with glutathione metabolism were found to be increased in abundance in stress conditions in all zones examined, including several isoforms of glutathione S-transferase which were observed at greatest abundance in Z3 in Azucena. Data analysis is ongoing, including characterization of functional marker proteins to verify expected metabolic processes overrepresented in each zone: cell division in Z1, cell wall expansion and vacuolarisation in Z2, and xylogenesis in Z3. Further details of all the differentially expressed proteins identified in each of the comparisons will be presented.