Phytochromes and cryptochromes regulate the differential growth of Arabidopsis hypocotyls in both a PGP19-dependent and a PGP19-independent manner.
ABSTRACT Photoreceptors, phytochromes and cryptochromes regulate hypocotyl growth under specific conditions, by suppressing negative gravitropism, modulating phototropism and inhibiting elongation. Although these effects seem to be partially caused via the regulation of the phytohormone auxin, the molecular mechanisms underlying this process are still poorly understood. In our present study, we demonstrate that the flabby mutation enhances both phytochrome- and cryptochrome-inducible hypocotyl bending in Arabidopsis. The FLABBY gene encodes the ABC-type auxin transporter, PGP19, and its expression is suppressed by the activation of phytochromes and cryptochromes. Our current results therefore indicate that the phytochromes and cryptochromes have at least two effects upon the tropic responses of the hypocotyls in Arabidopsis: the enhancement of hypocotyl bending through the suppression of PGP19, and a PGP19-independent mechanism that induces hypocotyl bending. By the using an auxin polar transport assay and DR5:GUS expression analysis, we further find that the phytochromes inhibit basipetal auxin transport, and induce the asymmetric distribution of auxin in the hypocotyls. These data suggest that the control of auxin transport by phytochromes and cryptochromes is a critical regulatory component of hypocotyl growth in response to light.
- SourceAvailable from: Philip B Brewer[show abstract] [hide abstract]
ABSTRACT: The plant hormone auxin plays crucial roles in regulating plant growth development, including embryo and root patterning, organ formation, vascular tissue differentiation and growth responses to environmental stimuli. Asymmetric auxin distribution patterns have been observed within tissues, and these so-called auxin gradients change dynamically during different developmental processes. Most auxin is synthesized in the shoot and distributed directionally throughout the plant. This polar auxin transport is mediated by auxin influx and efflux facilitators, whose subcellular polar localizations guide the direction of auxin flow. The polar localization of PIN auxin efflux carriers changes in response to developmental and external cues in order to channel auxin flow in a regulated manner for organized growth. Auxin itself modulates the expression and subcellular localization of PIN proteins, contributing to a complex pattern of feedback regulation. Here we review the available information mainly from studies of a model plant, Arabidopsis thaliana, on the generation of auxin gradients, the regulation of polar auxin transport and further downstream cellular events.Cellular and Molecular Life Sciences CMLS 01/2007; 63(23):2738-54. · 5.62 Impact Factor
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ABSTRACT: Many aspects of plant growth and development are dependent on the flow of the hormone auxin down the plant from the growing shoot tip where it is synthesized. The direction of auxin transport in stems is believed to result from the basal localization within cells of the PIN1 membrane protein, which controls the efflux of the auxin anion. Mutations in two genes homologous to those encoding the P-glycoprotein ABC transporters that are especially abundant in multidrug-resistant tumour cells in animals were recently shown to block polar auxin transport in the hypocotyls of Arabidopsis seedlings. Here we show that the mdr mutants display faster and greater gravitropism and enhanced phototropism instead of the impaired curvature development expected in mutants lacking polar auxin transport. We find that these phenotypes result from a disruption of the normal accumulation of PIN1 protein along the basal end of hypocotyl cells associated with basipetal auxin flow. Lateral auxin conductance becomes relatively larger as a result, enhancing the growth differentials responsible for tropic responses.Nature 07/2003; 423(6943):999-1002. · 38.60 Impact Factor
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ABSTRACT: When maize coleoptiles were unilaterally exposed to red light (7.9 micromol m(-2)s(-1) for 5 min), 3 h after treatment IAA levels in coleoptiles decreased in all regions, from top to basal, with levels about 60% of dark controls. Localized irradiation in the 5 mm top zone was sufficient to cause the same extent of IAA reduction in the tips to that in the tips of whole irradiated shoots. When coleoptiles were treated with N-1-naphthylphthalamic acid (NPA), an accumulation of IAA in the tip and a decrease of diffusible IAA from tips were simultaneously detected. IAA accumulation in red-light treated coleoptiles by NPA was much lower than that of dark controls. NPA treatment did not affect the content of conjugated IAA in either dark or light treated coleoptile tips. When (13)C(11) (15)N(2)-tryptophan (Trp) was applied to the top of coleoptiles, substantial amounts of stable isotope were incorporated into free IAA in dark and red-light treated coleoptile tips. The ratio of incorporation was slightly lower in red-light treated coleoptile tips than that in dark controls. The label could not be detected in conjugated IAA. The rate of basipetal transport of IAA was about 10 mm h(-1) and the velocity was not affected by red light. These results strongly suggest that red light does not affect the rates of conversion of free IAA to the conjugate form or of the basipetal transport, but just reduces the IAA level in the tips, probably inhibited by IAA biosynthesis from Trp in this region.Planta 12/2006; 224(6):1427-35. · 3.35 Impact Factor