Genetic Control and Phenotypic Plasticity of Root Cortical Aerenchyma in Maize

The functional role and genetic control of many root anatomical and architectural traits are poorly understood. Our research focuses on characterizing root traits for enhanced stress tolerance and identifying genetic mechanisms controlling the expression of root traits. We have identified a candidate gene for root cortical aerenchyma formation which mapped to a root cortex-expressed bHLH transcription factor gene. A bHLH121 Mu transposon mutant line and a CRISPR/Cas9 loss-of-function mutant exhibited reduced root cortical aerenchyma formation, whereas an overexpression line exhibited significantly greater root cortical aerenchyma formation when compared to the wildtype line in many environments. Overall functional validation of the bHLH121 gene’s importance in root cortical aerenchyma formation provides a functional marker to select varieties with improved soil exploration and thus yield. Characterization of these lines under suboptimal water and nitrogen availability in multiple soil environments revealed root cortical aerenchyma is plastic in response to abiotic stress. Our results suggest that phenotypic plasticity is highly quantitative and plasticity loci are distinct from loci that control trait expression in stress and non-stress conditions. The identification of genes and functional phenotypes of root traits will facilitate efforts for the development of novel nutrient and water efficient crop varieties.