The root system architecture (RSA) of crops can affect their production, particularly in abiotic stress conditions, such as with drought, waterlogging, and salinity. Salinity is a growing problem worldwide that negatively impacts on crop productivity, and it is believed that yields could be improved if RSAs that enabled plants to avoid saline conditions were identified. Here, we have demonstrated, through the cloning and characterization of qSOR1 (quantitative trait locus for SOIL SURFACE ROOTING 1), that a shallower root growth angle (RGA) could enhance rice yields in saline paddies. qSOR1 is negatively regulated by auxin, predominantly expressed in root columella cells, and involved in the gravitropic responses of roots. qSOR1 was found to be a homolog of DRO1 (DEEPER ROOTING 1), which is known to control RGA. CRISPR-Cas9 assays revealed that other DRO1 homologs were also involved in RGA. Introgression lines with combinations of gain-of-function and loss-of-function alleles in qSOR1 and DRO1 demonstrated four different RSAs (ultra-shallow, shallow, intermediate, and deep rooting), suggesting that natural alleles of the DRO1 homologs could be utilized to control RSA variations in rice. In saline paddies, near-isogenic lines carrying the qSOR1 loss-of-function allele had soil-surface roots (SOR) that enabled rice to avoid the reducing stresses of saline soils, resulting in increased yields compared to the parental cultivars without SOR. Our findings suggest that DRO1 homologs are valuable targets for RSA breeding and could lead to improved rice production in environments characterized by abiotic stress.

Water and nitrogen availability limit crop productivity globally more than most other environmental factors. Plant availability of macronutrients such as nitrate is, to a large extent, regulated by the amount of water available in the soil, and, during drought episodes, crops can become simultaneously water and nitrogen limited. In this review, we explore the intricate relationship between water and nitrogen transport in plants, from transpiration-driven mass flow in the soil to uptake by roots via membrane transporters and channels and transport to aerial organs. We discuss the roles of root architecture and of suberized hydrophobic root barriers governing apoplastic water and nitrogen movement into the vascular system. We also highlight the need to identify the signalling cascades regulating water and nitrogen transport, as well as the need for targeted physiological analyses of plant traits influencing water and nitrogen uptake. We further advocate for incorporation of new phenotyping technologies, breeding strategies, and agronomic practices to improve crop yield in water- and nitrogen-limited production systems.

Direct seeding saves time and labour in the cultivation of rice. However, seedling establishment is often unstable, and yields are lower than in transplanting. Anaerobic germination (AG) is a key trait for improvement of direct seeding of rice. We established a simple and reliable method of evaluating AG in rice breeding. We germinated seeds in distilled water or deoxygenated water and measured coleoptile length several days later; compared the results of each method with survival rate in flooded soil; and used the anoxic water method for QTL analysis and for testing cultivars. Coleoptile elongation in anoxic water and survival rate in flooded soil were significantly correlated (r = 0.879, P < 0.01). A significant QTL, likely to be a major gene (AG1), was found in chromosome segment substitution lines and in a backcrossed F 2 population derived from tolerant and sensitive lines. Diverse rice genetic resources were classified into tolerant or sensitive accession groups reflecting their ecotypes. Our study revealed that anoxic water evaluation method saves space and time in a stable environment compared with flooded soil evaluation. It is applicable to QTL analysis and isolation of genes underlying anaerobic germination.