Cortical parenchyma wall width regulates root metabolic cost and maize performance under suboptimal water...

Area of Science:

• Plant Biology
• Crop Science
• Genetics

Background:

• Maize (Zea mays) faces significant yield losses due to drought stress.
• Root traits influencing water use efficiency and stress tolerance are critical for crop improvement.
• Root cortical parenchyma wall width (CPW) is a potential but understudied trait for enhancing drought tolerance.

Purpose of the Study:

• To investigate the role of root cortical parenchyma wall width (CPW) in improving maize drought tolerance.
• To quantify the metabolic costs associated with CPW and its impact on root respiration.
• To evaluate the field performance of maize genotypes with contrasting CPW under water-limited conditions.

Main Methods:

• Functional-structural modeling (RootSlice) to predict metabolic costs of CPW.
• Field trials with maize genotypes differing in CPW under well-watered and water-stressed conditions.
• Physiological measurements including stomatal conductance, leaf CO2 assimilation, root respiration, biomass, and yield.
• Genome-wide association study (GWAS) to identify genes controlling CPW.

Main Results:

• Increased CPW (2 µm to 4 µm) predicted a ~15% reduction in root metabolic costs.
• Field data showed increased CPW correlated with 32-42% lower root respiration under water stress.
• Maize with wider CPW exhibited significantly enhanced drought tolerance, with up to 125% increased stomatal conductance, 325% increased CO2 assimilation, 73-78% increased shoot biomass, and 92-108% increased yield.
• Pleiotropy was suggested by CPW correlation with leaf mesophyll traits, and candidate genes for CPW were identified via GWAS.

Conclusions:

• Increased root CPW is a novel phene that enhances maize drought tolerance by reducing metabolic costs and improving physiological responses.
• Wider CPW confers substantial yield advantages under water stress, making it a promising target for breeding programs.
• Further research into CPW and its genetic basis is warranted for developing resilient maize varieties, with potential benefits also under nitrogen-limiting conditions.