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Biomedical subjects

J Chory

Publications and source records attributed to J Chory.

At least 19 recordsLinked to original sources
PubMed2001

BIG: a calossin-like protein required for polar auxin transport in Arabidopsis.

Polar auxin transport is crucial for the regulation of auxin action and required for some light-regulated responses during plant development. We have found that two mutants of Arabidopsis-doc1, which displays altered expression of light-regulated genes, and tir3, known for its reduced auxin transport-have similar defects and define mutations in a single gene that we have renamed BIG. BIG is very similar to the Drosophila gene Calossin/Pushover, a member of a gene family also present in Caenorhabditis elegans and human genomes. The protein encoded by BIG is extraordinary in size, 560 kD, and contains several putative Zn-finger domains. Expression-profiling experiments indicate that altered expression of multiple light-regulated genes in doc1 mutants can be suppressed by elevated levels of auxin caused by overexpression of an auxin biosynthetic gene, suggesting that normal auxin distribution is required to maintain low-level expression of these genes in the dark. Double mutants of tir3 with the auxin mutants pin1, pid, and axr1 display severe defects in auxin-dependent growth of the inflorescence. Chemical inhibitors of auxin transport change the intracellular localization of the auxin efflux carrier PIN1 in doc1/tir3 mutants, supporting the idea that BIG is required for normal auxin efflux.

Amino Acid Sequence↗
PubMed2001

BRI1 is a critical component of a plasma-membrane receptor for plant steroids.

Most multicellular organisms use steroids as signalling molecules for physiological and developmental regulation. Two different modes of steroid action have been described in animal systems: the well-studied gene regulation response mediated by nuclear receptors, and the rapid non-genomic responses mediated by proposed membrane-bound receptors. Plant genomes do not seem to encode members of the nuclear receptor superfamily. However, a transmembrane receptor kinase, brassinosteroid-insensitive1 (BRI1), has been implicated in brassinosteroid responses. Here we show that BRI1 functions as a receptor of brassinolide, the most active brassinosteroid. The number of brassinolide-binding sites and the degree of response to brassinolide depend on the level of BRI1 protein. The brassinolide-binding activity co-immunoprecipitates with BRI1, and requires a functional BRI1 extracellular domain. Moreover, treatment of Arabidopsis seedlings with brassinolide induces autophosphorylation of BRI1, which, together with our binding studies, shows that BRI1 is a receptor kinase that transduces steroid signals across the plasma membrane.

Arabidopsis↗
PubMed2001

Arabidopsis genomes uncoupled 5 (GUN5) mutant reveals the involvement of Mg-chelatase H subunit in plastid-to-nucleus signal transduction.

A plastid-derived signal plays an important role in the coordinated expression of both nuclear- and chloroplast-localized genes that encode photosynthesis-related proteins. Arabidopsis GUN (genomes uncoupled) loci have been identified as components of plastid-to-nucleus signal transduction. Unlike wild-type plants, gun mutants have nuclear Lhcb1 expression in the absence of chloroplast development. We observed a synergistic phenotype in some gun double-mutant combinations, suggesting there are at least two independent pathways in plastid-to-nucleus signal transduction. There is a reduction of chlorophyll accumulation in gun4 and gun5 mutant plants, and a gun4gun5 double mutant shows an albino phenotype. We cloned the GUN5 gene, which encodes the ChlH subunit of Mg-chelatase. We also show that gun2 and gun3 are alleles of the known photomorphogenic mutants, hy1 and hy2, which are required for phytochromobilin synthesis from heme. These findings suggest that certain perturbations of the tetrapyrrole biosynthetic pathway generate a signal from chloroplasts that causes transcriptional repression of nuclear genes encoding plastid-localized proteins. The comparison of mutant phenotypes of gun5 and another Mg-chelatase subunit (ChlI) mutant suggests a specific function for ChlH protein in the plastid-signaling pathway.

Amino Acid Sequence↗
PubMed2001

A role for flavin monooxygenase-like enzymes in auxin biosynthesis.

Although auxin is known to regulate many processes in plant development and has been studied for over a century, the mechanisms whereby plants produce it have remained elusive. Here we report the characterization of a dominant Arabidopsis mutant, yucca, which contains elevated levels of free auxin. YUCCA encodes a flavin monooxygenase-like enzyme and belongs to a family that includes at least nine other homologous Arabidopsis genes, a subset of which appears to have redundant functions. Results from tryptophan analog feeding experiments and biochemical assays indicate that YUCCA catalyzes hydroxylation of the amino group of tryptamine, a rate-limiting step in tryptophan-dependent auxin biosynthesis.

Alleles↗
PubMed2001

Steroid signaling in plants: from the cell surface to the nucleus.

Steroid hormones are signaling molecules important for normal growth, development and differentiation of multicellular organisms. Brassinosteroids (BRs) are a class of polyhydroxylated steroids that are necessary for plant development. Molecular genetic studies in Arabidopsis thaliana have led to the cloning and characterization of the BR receptor, BRI1, which is a transmembrane receptor serine/threonine kinase. The extracellular domain of BRI1, which is composed mainly of leucine-rich repeats, can confer BR responsivity to heterologous cells and is required for BR binding. Although downstream components of BR action are mostly unknown, multiple genes whose expression are regulated by BRs have been identified and suggest mechanisms by which BRs affect cell elongation and division.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Natural variation in light sensitivity of Arabidopsis.

Because plants depend on light for growth, their development and physiology must suit the particular light environment. Plants native to different environments show heritable, apparently adaptive, changes in their response to light. As a first step in unraveling the genetic and molecular basis of these naturally occurring differences, we have characterized intraspecific variation in a light-dependent developmental process-seedling emergence. We examined 141 Arabidopsis thaliana accessions for their response to four light conditions, two hormone conditions and darkness. There was significant variation in all conditions, confirming that Arabidopsis is a rich source of natural genetic diversity. Hierarchical clustering revealed that some accessions had response patterns similar to known photoreceptor mutants, suggesting changes in specific signaling pathways. We found that the unusual far-red response of the Lm-2 accession is due to a single amino-acid change in the phytochrome A (PHYA) protein. This change stabilizes the light-labile PHYA protein in light and causes a 100-fold shift in the threshold for far-red light sensitivity. Purified recombinant Lm-2 PHYA also shows subtle photochemical differences and has a reduced capacity for autophosphorylation. These biochemical changes contrast with previously characterized natural alleles in loci controlling plant development, which result in altered gene expression or loss of gene function.

Arabidopsis↗
PubMed2001

BIN2, a new brassinosteroid-insensitive locus in Arabidopsis.

Brassinosteroids (BRs) play important roles throughout plant development. Although many genes have been identified that are involved in BR biosynthesis, genetic approaches in Arabidopsis have led to the identification of only one gene, BRI1, that encodes a membrane receptor for BRs. To expand our knowledge of the molecular mechanism(s) of plant steroid signaling, we analyzed many dwarf and semidwarf mutants collected from our previous genetic screens and identified a semidwarf mutant that showed little response to exogenous BR treatments. Genetic analysis of the bin2 (BR-INSENSITIVE 2) mutant indicated that the BR-insensitive dwarf phenotype was due to a semidominant mutation in the BIN2 gene that mapped to the middle of chromosome IV between the markers CH42 and AG. A direct screening for similar semidwarf mutants resulted in the identification of a second allele of the BIN2 gene. Despite some novel phenotypes observed with the bin2/+ mutants, the homozygous bin2 mutants were almost identical to the well-characterized bri1 mutants that are defective in BR perception. In addition to the BR-insensitive dwarf phenotype, bin2 mutants exhibited BR insensitivity when assayed for root growth inhibition and feedback inhibition of CPD gene expression. Furthermore, bin2 mutants displayed an abscisic acid-hypersensitive phenotype that is shared by the bri1 and BR-deficient mutants. A gene dosage experiment using triploid plants suggested that the bin2 phenotypes were likely caused by either neomorphic or hypermorphic gain-of-function mutations in the BIN2 gene. Thus, the two bin2 mutations define a novel genetic locus whose gene product might play a role in BR signaling.

Arabidopsis↗
PubMed2001

ELF3 encodes a circadian clock-regulated nuclear protein that functions in an Arabidopsis PHYB signal transduction pathway.

Many aspects of plant development are regulated by photoreceptor function and the circadian clock. Loss-of-function mutations in the Arabidopsis EARLY FLOWERING 3 (ELF3) and PHYTOCHROME B (PHYB) genes cause early flowering and influence the activity of circadian clock-regulated processes. We demonstrate here that the relative abundance of the ELF3 protein, which is a novel nucleus-localized protein, displays circadian regulation that follows the pattern of circadian accumulation of ELF3 transcript. Furthermore, the ELF3 protein interacts with PHYB in the yeast two-hybrid assay and in vitro. Genetic analyses show that ELF3 requires PHYB function in early morphogenesis but not for the regulation of flowering time. This suggests that ELF3 is a component of a PHYB signaling complex that controls early events in plant development but that ELF3 and PHYB control flowering via independent signal transduction pathways.

Amino Acid Sequence↗
PubMed2000

Alteration of stimulus-specific guard cell calcium oscillations and stomatal closing in Arabidopsis det3 mutant.

Cytosolic calcium oscillations control signaling in animal cells, whereas in plants their importance remains largely unknown. In wild-type Arabidopsis guard cells abscisic acid, oxidative stress, cold, and external calcium elicited cytosolic calcium oscillations of differing amplitudes and frequencies and induced stomatal closure. In guard cells of the V-ATPase mutant det3, external calcium and oxidative stress elicited prolonged calcium increases, which did not oscillate, and stomatal closure was abolished. Conversely, cold and abscisic acid elicited calcium oscillations in det3, and stomatal closure occurred normally. Moreover, in det3 guard cells, experimentally imposing external calcium-induced oscillations rescued stomatal closure. These data provide genetic evidence that stimulus-specific calcium oscillations are necessary for stomatal closure.

Abscisic Acid↗
PubMed2000

Galactolipid deficiency and abnormal chloroplast development in the Arabidopsis MGD synthase 1 mutant.

The lipid monogalactosyl diacylglycerol (MGD) is a major structural component of photosynthetic membranes in chloroplasts. Its formation is catalyzed by the enzyme MGD synthase. In many plants, MGD derives from two different biosynthetic pathways: the prokaryotic pathway, which operates entirely within the plastid, and the eukaryotic pathway, which involves steps in the endoplasmic reticulum. Here, we describe the identification and characterization of an Arabidopsis mutant with a defective MGD synthase gene (MGD1). The mutant was identified in a screen of T-DNA lines for individuals with defects in chloroplast biogenesis. It has a yellow-green phenotype that correlates with a approximately 50% deficiency in total chlorophyll per plant. A single T-DNA insertion is located adjacent to the transcription initiation site of the MGD1 gene, and the abundance of MGD1 mRNA is reduced by 75% compared with wild type. Correlation between steady-state MGD1 transcript levels and MGD synthase activity (also reduced by 75% in mgd1) suggests that MGD1 is the most important MGD synthase in green tissues. The amount of MGD in mutant leaves is reduced by 42% compared with wild type. MGD from the mutant contains 23% less 16:3 fatty acid and 10% more 18:3 fatty acid. Because 16:3 is a characteristic feature of MGD from the prokaryotic pathway, it is possible that MGD1 operates with some preference in the prokaryotic pathway. Finally, the MGD-deficiency of mgd1 is correlated with striking defects in chloroplast ultrastructure, strongly suggesting a unique role for MGD in the structural organization of plastidic membranes.

Amino Acid Sequence↗
PubMed2000

Perception of brassinosteroids by the extracellular domain of the receptor kinase BRI1.

An assay was developed to study plant receptor kinase activation and signaling mechanisms. The extracellular leucine-rich repeat (LRR) and transmembrane domains of the Arabidopsis receptor kinase BRI1, which is implicated in brassinosteroid signaling, were fused to the serine/threonine kinase domain of XA21, the rice disease resistance receptor. The chimeric receptor initiates plant defense responses in rice cells upon treatment with brassinosteroids. These results, which indicate that the extracellular domain of BRI1 perceives brassinosteroids, suggest a general signaling mechanism for the LRR receptor kinases of plants. This system should allow the discovery of ligands for the LRR kinases, the largest group of plant receptor kinases.

Arabidopsis↗
PubMed2000

Regulation of auxin response by the protein kinase PINOID.

Arabidopsis plants carrying mutations in the PINOID (PID) gene have a pleiotropic shoot phenotype that mimics that of plants grown on auxin transport inhibitors or of plants mutant for the auxin efflux carrier PINFORMED (PIN), with defects in the formation of cotyledons, flowers, and floral organs. We have cloned PID and find that it is transiently expressed in the embryo and in initiating floral anlagen, demonstrating a specific role for PID in promoting primordium development. Constitutive expression of PID causes a phenotype in both shoots and roots that is similar to that of auxin-insensitive plants, implying that PID, which encodes a serine-threonine protein kinase, negatively regulates auxin signaling.

Amino Acid Sequence↗