Auxin coreceptor IAA17/AXR3 controls cell elongation in Arabidopsis thaliana root by modulation of auxin and gibberellin perception

Proper functioning of the nuclear auxin pathway is essential for regulating plant growth and development by maintaining auxin homeostasis. To understand better physiological mechanisms involved in auxin signaling pathways we investigated the localization and effect of accumulation of auxin coreceptor IAA17/AXR3 in root. We demonstrate that the accumulation of stable nuclear AXR3-1 protein interferes with auxin homeostasis, causing auxin insensitivity and increased rapid root cell elongation followed by detained growth. This growth pattern is associated with changes in phytohormone gene expression. Data from transcriptomic screen combined with reporter lines and mutant studies declare essential role of auxin homeostasis in maintaining optimal root growth rate and development. We proposed a model in which rapid cell elongation is caused by combination of AXR3-1-dependent auxin insensitivity associated with unblocked gibberellin effect on root. This study demonstrate that plants coordinate gibberellin homeostasis by the auxin signaling pathway, contributing to avoid excessive root elongation. Comparative gene expression profiling analysis of RNA-seq data from 2 lines inducible overexpressing stable form of auxin coreceptor AXR3-1 and from Col-0 treated with IAA (3-indoleacetic acid; Sigma-Aldrich), PEO-IAA (2-(1H-Indol-3-yl)-4-oxo-4-phenyl-butyric acid ; MedChemExpress) and mock (ethanol). Experimental material was lines expressing stable form of AXR3-1 under estradiol inducible promoter (line g1090 promoter g1090::XVE>>AXR3-1-mCherry (10.1038/nature13663)) and under heat shock promoter (line HS::AXR3-1 (10.1242/dev.00659)) in Col-0 background. Each of these lines has an appropriate control (treated in the same way as the mutant line, it means Col-0 treated with estradiol or heat shock). RNA from 50 Arabidopsis thaliana root tips (1-2 mm) were extracted, 3 biological replicas were used.