Auxin signaling under abiotic stress conditions

Abstract

Root system architecture (RSA) plasticity is a key property that enables plants to cope with a variety of abiotic stresses. The development of lateral root is known to be a major determinant of RSA and is reduced during abiotic stresses because of decreased auxin responses. It has been reported that the auxin distribution and the expression of auxin signaling regulators are changed under abiotic stress conditions to reduce the auxin responses. However, the molecular function of auxin signaling regulator proteins during stress conditions is poorly understood. Here, I show that the nucleo-cytoplasmic distribution of AUXIN/INDOLE-3-ACETIC ACID INDUCIBLE (AUX/IAA) 12/19 proteins, negative regulators of auxin signaling, determines lateral root development. Cytoplasmic localization of IAA12/19 proteins in the elongation zone of roots enforces auxin signaling output, thus enabling lateral root development. Among nuclear pore complex (NPC) components, CONSTITUTIVE EXPRESSOR OF PATHOGENESIS-RELATED GENES 5 (CPR5) selectively mediates cytoplasmic translocation of IAA12/19 proteins. Under abiotic stress conditions, CPR5 expression is significantly reduced resulting in accumulation of nuclear-localized IAA12/19 proteins in the elongation zone and suppression of lateral root development, which is reiterated in the cpr5 mutant. Therefore, this study reveals a new regulatory mechanism of auxin signaling in which the spatial distribution of AUX/IAA regulators is critical for lateral root development, especially in fluctuating environmental condition.