Imaging-based Genome-Wide Association Study Identifies Medicago GOLVEN10 As a Regulator of Root Angle Traits and Reveals Antagonism by Ethylene in Root Tortuosity.

Root system architecture affects water and mineral uptake and is important for plant adaptation to fluctuating nutrient availability. Small signaling peptides and their receptors influence root traits associated with macronutrient uptake. In this study, genome-wide association analyses were performed using 2D images of agar plate-grown Medicago truncatula accessions to understand the impact of GOLVEN10 peptide (GLV10) treatment on three root traits: root tortuosity, lateral root (LR) branch angle, and the gravity setpoint angle (GSA). Upon GLV10 treatment, roots of wild-type M. truncatula Jemalong A17 and R108 accessions showed increased primary root coiling (or tortuosity), increased LR branch angle, and reduced GSA. We identified 88 significant single nucleotide polymorphisms (SNPs) associated with these traits in GLV10-treated plants, distinct from the 163 SNPs in untreated plants. Importantly, the ethylene regulatory pathway was implicated in root tortuosity and LR emergence relative to the primary root. Application of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid reduced root sensitivity to GLV10, while the ethylene signaling mutant sickle was hypersensitive, indicating that GLV10 and ethylene pathways act antagonistically to control root tortuosity. These findings have implications for root gravitropic responses, and the ability of roots to penetrate deeper soil layers for nutrients and water.