Auxin biosynthesis: Spatial regulation and adaptation to stress

The plant hormone auxin is essential for plant growth and development, controlling both organ development and overall plant architecture. Auxin homeostasis is regulated by coordination of biosynthesis, transport, conjugation, sequestration/storage, and catabolism to optimize concentration-dependent growth responses and adaptive responses to temperature, water stress, herbivory and pathogens. At present, the best defined pathway of auxin biosynthesis is the TAA/YUC route, in which the tryptophan aminotransferases TAA and TAR and YUCCA flavin-dependent monooxygenases produce the auxin indole-3-acetic acid from tryptophan. This review highlights recent advances in our knowledge of TAA/YUC-dependent auxin biosynthesis focussing on membrane localisation of auxin biosynthetic enzymes, differential regulation in root and shoot tissue, and auxin biosynthesis during abiotic stress

Brachytic2/ZmABCB1 functions in IAA export from intercalary meristems

Dwarfism traits in Zea mays are regulated by multiple factors including the hormone auxin. Dwarf brachytic2 (br2) mutants harbour lesions in the gene encoding an orthologue of Arabidopsis thaliana ABCB1 which functions in auxin efflux out of meristematic regions in the shoot and root. br2 mesocotyls and coleoptiles exhibit reduced auxin transport. However, the dwarf stature of br2 derives from shortened lower internodes whilst the upper portion of the plant is completely normal. As such, it is counter-intuitive to attribute br2 dwarfism exclusively to reduced auxin export out of the shoot apex. Arabidopsis abcb1 mutants exhibit only minor reductions in auxin transport and plant height unless combined with mutations in the ABCB19 auxin transporter. Phylogenetic modelling analysis excludes the possibility that BR2 is more closely related to ABCB19 which has three more closely related orthologues in maize. BR2 is expressed in nodal meristems, and analyses of auxin transport and content indicate that BR2 function in these grass-specific tissues is analogous to ABCB1 function in the shoot and root apex of Arabidopsis. These results indicate that ABCB1/BR2 function is conserved between dicots and monocots, but also suggests that this function must be understood in the context of the segmental organization of grass plants

Early-type galaxies in the SDSS. I. The sample

A sample of nearly 9000 early-type galaxies, in the redshift range 0.01 < z < 0.3, was selected from the Sloan Digital Sky Survey using morphological and spectral criteria. This paper describes how the sample was selected, presents examples of images and seeing corrected fits to the observed surface brightness profiles, describes our method for estimating K-corrections, and shows that the SDSS spectra are of sufficiently high quality to measure velocity dispersions accurately. It also provides catalogs of the measured photometric and spectroscopic parameters. In related papers, these data are used to study how early-type galaxy observables, including luminosity, effective radius, surface brightness, color, and velocity dispersion, are correlated with one another.Comment: 63 pages, 21 figures. Accepted by AJ (scheduled for April 2003). This paper is part I of a revised version of astro-ph/0110344. The full version of Tables 2 and 3, i.e. the tables listing the photometric and spectroscopic parameters of ~ 9000 galaxies, are available at http://astrophysics.phys.cmu.edu/~bernardi/SDSS/Etypes/TABLE

Cellular efflux of auxin catalyzed by the Arabidopsis MDR/PGP transporter AtPGP1

Directional transport of the phytohormone auxin is required for the establishment and maintenance of plant polarity, but the underlying molecular mechanisms have not been fully elucidated. Plant homologs of human multiple drug resistance/P-glycoproteins (MDR/PGPs) have been implicated in auxin transport, as defects in MDR1 (AtPGP19) and AtPGP1 result in reductions of growth and auxin transport in Arabidopsis (atpgp1, atpgp19), maize (brachytic2) and sorghum (dwarf3). Here we examine the localization, activity, substrate specificity and inhibitor sensitivity of AtPGP1. AtPGP1 exhibits non-polar plasma membrane localization at the shoot and root apices, as well as polar localization above the root apex. Protoplasts from Arabidopsis pgp1 leaf mesophyll cells exhibit reduced efflux of natural and synthetic auxins with reduced sensitivity to auxin efflux inhibitors. Expression of AtPGP1 in yeast and in the standard mammalian expression system used to analyze human MDR-type proteins results in enhanced efflux of indole-3-acetic acid (IAA) and the synthetic auxin 1-naphthalene acetic acid (1-NAA), but not the inactive auxin 2-NAA. AtPGP1-mediated efflux is sensitive to auxin efflux and ABC transporter inhibitors. As is seen in planta, AtPGP1 also appears to mediate some efflux of IAA oxidative breakdown products associated with apical sites of high auxin accumulation. However, unlike what is seen in planta, some additional transport of the benzoic acid is observed in yeast and mammalian cells expressing AtPGP1, suggesting that other factors present in plant tissues confer enhanced auxin specificity to PGP-mediated transport. © 2005 Blackwell Publishing Ltd

Early-type galaxies in the SDSS. III. The Fundamental Plane

A magnitude limited sample of nearly 9000 early-type galaxies, in the redshift range 0.01 < z < 0.3, was selected from the Sloan Digital Sky Survey using morphological and spectral criteria. The Fundamental Plane relation in this sample is R_o ~ sigma^{1.49\pm 0.05} I_o^{-0.75\pm 0.01} in the r* band. It is approximately the same in the g*, i* and z* bands. Relative to the population at the median redshift in the sample, galaxies at lower and higher redshifts have evolved only little. If the Fundamental Plane is used to quantify this evolution then the apparent magnitude limit can masquerade as evolution; once this selection effect has been accounted for, the evolution is consistent with that of a passively evolving population which formed the bulk of its stars about 9 Gyrs ago. One of the principal advangtages of the SDSS sample over previous samples is that the galaxies in it lie in environments ranging from isolation in the field to the dense cores of clusters. The Fundamental Plane shows that galaxies in dense regions are slightly different from galaxies in less dense regions.Comment: 27 pages, 10 figures. Accepted by AJ (scheduled for April 2003). This paper is part III of a revised version of astro-ph/011034

Early-type galaxies in the SDSS. IV. Colors and chemical evolution

The colors and chemical abundances of early-type galaxies at redshifts z<0.3 are studied using a sample of nearly 9000 galaxies, selected from the Sloan Digital Sky Survey using morphological and spectral criteria. In this sample, redder galaxies have larger velocity dispersions. Color also correlates with magnitude and size, but these correlations are entirely due to the L-sigma and R_o-sigma relations: the primary correlation is color-sigma. The red light in early-type galaxies is, on average, slightly more centrally concentrated than the blue. Because of these color gradients, the strength of the color--magnitude relation depends on whether or not the colors are defined using a fixed metric aperture. Chemical evolution and star formation histories of early-type galaxies are investigated using co-added spectra of similar objects. At fixed sigma, the population at z ~ 0.2 had weaker Mg_2 and stronger H_beta absorption compared to the population at z ~ 0. It was also bluer. Comparison of these colors and line-strengths, and their evolution, with single-burst stellar population models suggests a formation time of 9 Gyrs ago, consistent with a Fundamental Plane analysis of this sample.Comment: 38 pages, 16 figures. Accepted by AJ (scheduled for April 2003). This paper is part IV of a revised version of astro-ph/0110344. The full version of Table 3 and the 182 composite spectra can be downloaded from http://astrophysics.phys.cmu.edu/~bernardi/SDSS/Etypes/SPECFITS A README file (bernardi4.README) explains the content of the director

The Seventh Data Release of the Sloan Digital Sky Survey

This paper describes the Seventh Data Release of the Sloan Digital Sky Survey (SDSS), marking the completion of the original goals of the SDSS and the end of the phase known as SDSS-II. It includes 11663 deg^2 of imaging data, with most of the roughly 2000 deg^2 increment over the previous data release lying in regions of low Galactic latitude. The catalog contains five-band photometry for 357 million distinct objects. The survey also includes repeat photometry over 250 deg^2 along the Celestial Equator in the Southern Galactic Cap. A coaddition of these data goes roughly two magnitudes fainter than the main survey. The spectroscopy is now complete over a contiguous area of 7500 deg^2 in the Northern Galactic Cap, closing the gap that was present in previous data releases. There are over 1.6 million spectra in total, including 930,000 galaxies, 120,000 quasars, and 460,000 stars. The data release includes improved stellar photometry at low Galactic latitude. The astrometry has all been recalibrated with the second version of the USNO CCD Astrograph Catalog (UCAC-2), reducing the rms statistical errors at the bright end to 45 milli-arcseconds per coordinate. A systematic error in bright galaxy photometr is less severe than previously reported for the majority of galaxies. Finally, we describe a series of improvements to the spectroscopic reductions, including better flat-fielding and improved wavelength calibration at the blue end, better processing of objects with extremely strong narrow emission lines, and an improved determination of stellar metallicities. (Abridged)Comment: 20 pages, 10 embedded figures. Accepted to ApJS after minor correction

The role of multidrug resistance-like/P-glycoproteins in auxin transport

Directional transport of the phytohormone auxin is required for the establishment and maintenance of plant polarity, but the underlying molecular mechanisms have not been fully elucidated. Recently, plant orthologs of human multiple drug resistance/P-glycoproteins (MDR/PGPs) have been implicated, as defective PGP19 (MDR1) and PGP1 resulted in reductions in growth and auxin transport of varying severity in Arabidopsis (pgp1, pgp19), maize (brachytic2), and sorghum (dwarf3). Auxin transport defects and dwarf phenotypes are more exaggerated in pgp1 pgp19 double mutants, suggesting overlapping function. Previous studies suggested that PGPs stabilize PIN protein localization on the plasma membrane, but did not determine whether PGPs could directly mediate auxin transport at the cellular level. Arabidopsis pgp1, pgp19, and pgp1 pgp19 protoplasts displayed reductions in the transport of natural and synthetic auxins and oxidative auxin breakdown products consistent with the defects in auxin transport observed in whole plants and seedlings. Heterologous expression of PGP1 and PGP19 in yeast and mammalian cells resulted in increased auxin efflux, while expression of PGP4 resulted in auxin influx. PGPs expressed in mammalian cells also transported synthetic auxins, oxidative auxin breakdown products, and benzoic acid, but failed to transport mammalian multiple drug resistance substrates. These data indicate that in plants PGPs do not function as multiple-drug resistance proteins, but instead function as ATP-dependent hydrophobic anion transporters. Synergistic increases in auxin efflux resulted when PGPI and PGP19 were coexpressed with the PIN1 auxin efflux facilitator. An antagonistic interaction between PIN2, which appeared to activate auxin efflux activity of mammalian organic acid transporters, and PGP1 and PGP19 was also seen. PGP4 demonstrated an antagonistic interaction with PIN1, but a synergistic interaction with PIN2. PGP-PIN coexpression resulted in increased transport specificity and sensitivity to auxin transport inhibitors. PGP-PIN interactions were confirmed using yeast two-hybrid and co-immunoprecipitation assays, and PIN1 and PGP19 were found to co-localize in detergent resistant lipid raft membrane microdomains. PGP19 appears to stabilize PIN1 in these structures, as PIN1 was preferentially detergent-solubilized from pgp19 membranes, providing a rationale for the mislocalization of PIN1 previously observed in detergent-treated pgp19 hypocotyls

Generation of an Attenuated, Cross-Protective \u3ci\u3ePepino mosaic virus\u3c/i\u3e Variant Through Alignment-Guided Mutagenesis of the Viral Capsid Protein

Mild variants of many viruses are able to protect infected plants from subsequent invasion by more severe variants of the same viruses through a process known as cross-protection. In the past, the cross-protective viral variants were commonly derived from mild field isolates that were sometimes genetically heterogeneous, providing variable levels of crossprotection. Here, we report a novel approach to rapidly generate crossprotective variants of the tomato-infecting Pepino mosaic virus (PepMV) independently of the availability of mild field isolates. Our approach sought to attenuate PepMV by mutating less conserved amino acid residues of the abundantly produced capsid protein (CP). These less-conserved amino acid residues were identified through multiple alignments of CPs of six potexviruses including PepMV, and were altered systematically to yield six PepMV mutants. These mutants were subsequently inoculated onto the model plant Nicotiana benthamiana, as well as tomato, to evaluate their accumulation levels, symptom severities, and cross-protection potentials. The mutant KD, in which the threonine (T) and alanine (A) residues at CP positions 66 and 67 were replaced with lysine (K) and aspartic acid (D), respectively, were found to accumulate to low levels in infected plants, cause very mild symptoms, and effectively protect both N. benthamiana and tomato against secondary infections by wild-type PepMV. These data suggest that our approach represents a simple, fast, and reliable way of generating attenuated viral variants capable of cross-protection