Roles for IBA-derived auxin in plant development

Abstract

The plant hormone auxin is a central regulator of plant growth and development. Because auxin plays critical roles in cell division and cell expansion, plants use a number of cellular mechanisms to regulate auxin levels and response. Among these mechanisms is regulated input from the auxin precursor indole-3-butyric acid (IBA) toward the pool of active auxin [indole-3-acetic acid (IAA)]. In this review, we cover the mechanisms of IBA transport and conversion, and discuss specific roles for IBA-derived auxin in driving certain developmental events. We further discuss multiple open questions remaining for the IBA field.

Keywords: Auxin; IBA; plant development; root development; shoot development.

Fig. 1.

IAA and IBA. The side chain in the 3 position on the indole ring of IBA has four carbons, as opposed to the two-carbon side chain of IAA.

Fig. 2.

Cellular model of IAA and IBA transport. IAA and IBA use distinct transporters for movement into and out of cells and into and out of the peroxisome.

Fig. 3.

IBA-derived auxin drives lateral root development. In addition to roles for IBA-derived auxin originating in the lateral root cap (De Rybel et al., 2012; Xuan et al., 2015), IBA to IAA conversion in the lateral root primordia themselves also likely contributes to lateral root development (Strader et al., 2011). (This figure is available in colour at JXB online.)

Fig. 4.

Genes encoding IBA conversion enzymes are regulated by various stresses. Relative transcript levels of ECH2, IBR1, IBR3, and IBR10 obtained from the eFP Browser database (Schmid et al., 2005; Winter et al., 2007) in response to (A) hormone treatment, (B) biotic stress, (C) abiotic stress in shoots, or (D) abiotic stress in roots.