Re-engineering root system architecture for steeper and deeper rooting in cereals

Steeper and deeper plant root system architecture is predicted to increase uptake of water and nitrogen soil resources, in addition to improving drought avoidance and carbon sequestration. Soil resource uptake is a major root system function determined by the spatial arrangement of roots. Gravitropism describes plant growth in response to gravity and root gravitropic responses strongly influence root system architecture development. The goal of this work was to investigate mechanisms and genes underlying cereal root system architecture for achieving steeper and deeper rooting. This work investigated phenotyping methods and the variation in root system architecture in wheat varieties and landraces, and gravitropic setpoint angle maintenance in wheat and rice lateral roots. Auxin plays a central role in gravitropism and the absence of an auxin reporter in wheat initiated the development of a wheat DII-VENUS auxin reporter.
Root gravitropic mechanisms and genes have been extensively studied in many plant species but limited research has been translated into wheat. The LAZY gene family have important functions in regulating root and shoot growth angles. Nine wheat LAZY homoeologs have been discovered, now named the LAZY1, DRO1 and qSOR1 A, B and D homoeologs. Extended domain III (D3X) was characterised in wheat, as D3X is an important LAZY domain for Arabidopsis lateral root growth angle control, with D3X mutations inducing a steeper lateral root phenotype. Extended domain III mutations in D3X-containing wheat LAZY genes were introduced via transformation or in a TILLING background. These wheat mutants had steeper seminal roots, suggesting wheat lateral root growth angle may be controlled by a different mechanism. These findings have important implications for utilising the LAZY gene family in crop root system architecture modification. Overall, this work addressed gaps in the understanding of cereal root growth angle control and made new discoveries in the functions of the wheat LAZY gene family, contributing towards achieving steeper and deeper root system architecture for crop yield improvement in a changing climate.