Challenges to design-oriented breeding of root system architecture adapted to climate change

Abstract

Roots are essential organs for capturing water and nutrients from the soil. In particular, root system architecture (RSA) determines the extent of the region of the soil where water and nutrients can be gathered. As global climate change accelerates, it will be important to improve belowground plant parts, as well as aboveground ones, because roots are front-line organs in the response to abiotic stresses such as drought, flooding, and salinity stress. However, using conventional breeding based on phenotypic selection, it is difficult to select breeding lines possessing promising RSAs to adapted to abiotic stress because roots remain hidden underground. Therefore, new breeding strategies that do not require phenotypic selection are necessary. Recent advances in molecular biology and biotechnology can be applied to the design-oriented breeding of RSA without phenotypic selection. Here I summarize recent progress in RSA ideotypes as "design" and RSA-related gene resources as "materials" that will be needed in leveraging these technologies for the RSA breeding. I also highlight the future challenges to design-oriented breeding of RSA and explore solutions to these challenges.

Keywords: DRO1; QTL; edaphic stress; qSOR1; root plasticity; root robustness.

Fig. 1.

Concept of design-oriented breeding based on the different features between crossbreeding and industrial product development.

Fig. 2.

Promising ideotypes of root system architectures adapted to abiotic stresses. In each panel A–F, left and right figures represent regular and paddy fields, respectively. Each panel shows schematic models of the ideal root system architecture under a different abiotic stress condition. Plants shown are maize and rice—i.e., representative monocot crops—grown in regular and paddy fields, respectively. N, nitrogen; P, phosphorous. Question marks in the figure mean that no RSA ideotype have been established based on field studies.

Fig. 3.

Proposed regulatory pathways of gravity-induced root bending via DRO1 homologs in rice. Term in parentheses indicates the major tissues expressing each gene. DEZ, distal elongation zone.