Localized Induction of the ATP-Binding Cassette B19 Auxin Transporter Enhances Adventitious Root Formation in Arabidopsis

Abstract

Adventitious roots emerge from aerial plant tissues, and the induction of these roots is essential for clonal propagation of agriculturally important plant species. This process has received extensive study in horticultural species but much less focus in genetically tractable model species. We have explored the role of auxin transport in this process in Arabidopsis (Arabidopsis thaliana) seedlings in which adventitious root initiation was induced by excising roots from low-light-grown hypocotyls. Inhibition of auxin transport from the shoot apex abolishes adventitious root formation under these conditions. Root excision was accompanied by a rapid increase in radioactive indole-3-acetic acid (IAA) transport and its accumulation in the hypocotyl above the point of excision where adventitious roots emerge. Local increases in auxin-responsive gene expression were also observed above the site of excision using three auxin-responsive reporters. These changes in auxin accumulation preceded cell division events, monitored by a cyclin B1 reporter (pCYCB1;1:GUS), and adventitious root initiation. We examined excisioninduced adventitious root formation in auxin influx and efflux mutants, including auxin insensitive1, pin-formed1 (pin1), pin2, pin3, and pin7, with the most profound reductions observed in ATP-binding cassette B19 (ABCB19). An ABCB19 overexpression line forms more adventitious roots than the wild type in intact seedlings. Examination of transcriptional and translational fusions between ABCB19 and green fluorescent protein indicates that excision locally induced the accumulation of ABCB19 transcript and protein that is temporally and spatially linked to local IAA accumulation leading to adventitious root formation. These experiments are consistent with localized synthesis of ABCB19 protein after hypocotyl excision leads to enhanced IAA transport and local IAA accumulation driving adventitious root formation.

Nitric oxide mediates strigolactone signaling in auxin and ethylene-sensitive lateral root formation in sunflower seedlings

“…23 Mutants or treatments resulting in disturbed polar auxin transport show reduced AR formation. 37,38 While auxins and auxin signaling are essential for all stages of LR development, 39-42 exogenous auxin stimulates during the first stage and inhibits later developmental stages of AR formation, [43][44][45] thus indicating different sensitivity of both root-types to exogenous auxin. Besides exogenous or newly biosynthesized auxin, auxin transport, through the ABC-type multidrug-resistance ABCB19 transporter, is also essential for AR induction in hypocotyls.…”

“…Besides exogenous or newly biosynthesized auxin, auxin transport, through the ABC-type multidrug-resistance ABCB19 transporter, is also essential for AR induction in hypocotyls. 38 Earlier reports on auxin-SL interaction in regulating adventitious root initiation have revealed the role of SL in reducing adventitious root initiation through its negative impact on auxin levels in the cells of pericycle.…”

Block of ATP-Binding Cassette B19 Ion Channel Activity by 5-Nitro-2-(3-Phenylpropylamino)-Benzoic Acid Impairs Polar Auxin Transport and Root Gravitropism

“…Outgrowth of lateral roots, although not their initiation, depends significantly on ABCB19-mediated tipward auxin transport . The emergence of adventitious roots at the base of hypocotyls from which roots have been excised from Arabidopsis seedlings depends strongly on ABCB19-mediated auxin accumulation at the sites of primordium initiation (Sukumar et al, 2013).…”

Branching Out in Roots: Uncovering Form, Function, and Regulation

“…Auxin transporters are also important for adventitious root formation, with both influx (LAX3) and efflux (PIN1) carriers required for auxin accumulation in the early stages of adventitious root organogenesis (Della Rovere et al, 2013). An ATP-binding cassette transporter mediating IAA efflux (ABCB19) has also been linked to adventitious root formation (Sukumar et al, 2013). Other members of the same family have been shown to transport the auxin precursor indole-3-butyric acid (Ruzicka et al, 2010;Strader and Bartel, 2011), which, among all tested auxin isoforms, has the highest competence to induce adventitious root formation (Nordström et al, 1991).…”