It is shown that auxin accumulates asymmetrically during differential growth in an efflux-dependent manner and that actin-dependent relocalization of PIN3 in response to gravity provides a mechanism for redirecting auxin flux to trigger asymmetric growth.
Abstract:
Long-standing models propose that plant growth responses to light or gravity are mediated by asymmetric distribution of the phytohormone auxin. Physiological studies implicated a specific transport system that relocates auxin laterally, thereby effecting differential growth; however, neither the molecular components of this system nor the cellular mechanism of auxin redistribution on light or gravity perception have been identified. Here, we show that auxin accumulates asymmetrically during differential growth in an efflux-dependent manner. Mutations in the Arabidopsis gene PIN3, a regulator of auxin efflux, alter differential growth. PIN3 is expressed in gravity-sensing tissues, with PIN3 protein accumulating predominantly at the lateral cell surface. PIN3 localizes to the plasma membrane and to vesicles that cycle in an actin-dependent manner. In the root columella, PIN3 is positioned symmetrically at the plasma membrane but rapidly relocalizes laterally on gravity stimulation. Our data indicate that PIN3 is a component of the lateral auxin transport system regulating tropic growth. In addition, actin-dependent relocalization of PIN3 in response to gravity provides a mechanism for redirecting auxin flux to trigger asymmetric growth.
TL;DR: It is shown that organ formation in Arabidopsis involves dynamic gradients of the signaling molecule auxin with maxima at the primordia tips, which suggest that PIN-dependent, local auxin gradients represent a common module for formation of all plant organs, regardless of their mature morphology or developmental origin.
TL;DR: Nearly six decades after the structural elucidation of IAA, many aspects of auxin metabolism, transport and signalling are well established; however, more than a few fundamental questions and innumerable details remain unresolved.
TL;DR: This work shows that five PIN genes collectively control auxin distribution to regulate cell division and cell expansion in the primary root and reveals an interaction network of auxin transport facilitators and root fate determinants that control patterning and growth of the root primordium.
TL;DR: The results indicate how the establishment of cell polarity, polar auxin efflux and local auxin response result in apical–basal axis formation of the embryo, and thus determine the axiality of the adult plant.
TL;DR: It is shown that proteins involved in auxin transport regulate phyllotaxis, and data indicate that auxin is transported upwards into the meristem through the epidermis and the outermostMeristem cell layer.
TL;DR: Cotransfection experiments with natural and synthetic AuxRE reporter genes and effector genes encoding Aux/IAA proteins showed that overexpression of Aux/ IAA proteins in carrot protoplasts resulted in specific repression of TGTCTC Auxre reporter gene expression.
TL;DR: The PIN-FORMED (PIN1) gene was found to encode a 67-kilodalton protein with similarity to bacterial and eukaryotic carrier proteins, and the AtPIN1 protein was detected at the basal end of auxin transport-competent cells in vascular tissue.
TL;DR: It is shown that the seemingly static localization of PIN1 results from rapid actin-dependent cycling between the plasma membrane and endosomal compartments, suggesting that PIN1 cycling is of central importance for auxin transport and that Auxin transport inhibitors affect efflux by generally interfering with membrane-trafficking processes.
TL;DR: Characterization of lateral root development in the shoot meristemless1 mutant demonstrates that root basipetal and leaf acropetal auxin transport activities are required during the initiation and emergence phases, respectively, of lateralRoot development.
TL;DR: The results suggest that AtPIN2 plays an important role in control of gravitropism regulating the redistribution of auxin from the stele towards the elongation zone of roots.
Q1. What contributions have the authors mentioned in the paper "Lateral relocation of auxin efflux regulator pin3 mediates tropism in arabidopsis" ?
The authors thank B. Diamond, J. Warner, M. Goodman and R. Laskov for critical review of the manuscript, and A. Bothwell for providing the P1-5 hybridoma. This work was supported by grants from the National Institutes of Health to P. D. B., to C. J. W. and to M. D. S., who is also supported by the Harry Eagle chair provided by the National Women ’ s Division of the Albert Einstein College of Medicine.
Q2. What is the role of auxin in the growth of Arabidopsis hypocoty?
Polar auxin transport represent a plausible means of lateral auxin distribution, as its chemical inhibition affects differential growth responses such as tropisms and apical hook formation7,8.
Q3. What is the effect of the polar auxin transport inhibitors on the apn?
Reduced naphthylphthalamic acid binding in the tir3 mutant of Arabidopsis isassociated with a reduction in polar auxin transport and diverse morphological defects.
Q4. What is the role of PIN3 in the morphology of the root columella?
In the root columella, PIN3 is positioned symmetrically at the plasma membrane but rapidly relocalizes laterally on gravity stimulation.
Q5. What is the asymmetric distribution of PIN3?
The authors show that asymmetric growth correlates with auxin efflux-dependent asymmetric auxin distribution and requires laterally localized PIN3 protein.
Q6. What is the lateral auxin transport system?
Developmental requirements for PIN3, its localization, as well as the proposed biochemical function for PIN proteins make PIN3 a likely candidate for an efflux component of the lateral auxin transport system.
Q7. What is the asymmetry of the PIN3 localization in columella cells?
in contrast to PIN1, was frequently detected in vesicles, suggesting that PIN3 cycles more rapidly or that the equilibrium of intracellular PIN3 pools is shifted more in favour of the internalized PIN3 pool.
Q8. What is the asymmetric distribution of auxin1 in plants?
Long-standing models propose that plant growth responses to light or gravity are mediated by asymmetric distribution of the phytohormone auxin1 – 3.
Q9. What is the mechanism of auxin flux in the columella cells?
Thus PIN3 is redirected towards one side of the columella cells and determines direction of auxin flux, which leads to asymmetric auxin accumulation and differential growth.
Q10. What is the role of auxin in the growth of the shoot?
These results show that asymmetric growth of the shoot correlates with auxin efflux-dependent asymmetric auxin distribution, and implicate the existence of auxin efflux components involved in asymmetric growth responses.