Table of Contents
IN BRIEF
RESEARCH ARTICLES
- A Conserved Mechanism of Bract Suppression in the Grass Family
Bract suppression in maize, rice, and barley is regulated by a conserved genetic mechanism. Interestingly, the orthologous gene in Arabidopsis has no role in bract suppression, suggesting distinct bract suppression mechanisms have evolved in these two lineages.
- Sieve Tube Geometry in Relation to Phloem Flow
This work describes a novel method for imaging cell anatomy and cell wall features by scanning electron microscopy. The method was used to image sieve plates and sieve element geometry at high resolution to correlate sieve tube–specific conductivity with phloem flow measurements.
- PSEUDO-RESPONSE REGULATORS 9, 7, and 5 Are Transcriptional Repressors in the Arabidopsis Circadian Clock
PSEUDORESPONSE REGULATOR9 (PRR9), PRR7, and PRR5 regulate the Arabidopsis circadian clock. PRR9, PRR7, and PRR5 proteins associate with CIRCADIAN CLOCK ASSOCIATED1 and LATE ELONGATED HYPOCOTYL promoters in a sequential manner to repress their expression. A conserved region common to the three PRR proteins is sufficient for repressor activity.
- F-Box Proteins FKF1 and LKP2 Act in Concert with ZEITLUPE to Control Arabidopsis Clock Progression
In Arabidopsis thaliana, the F-box protein ZTL affects the period length of the circadian clock by regulating the stability of the core clock proteins TOC1 and PRR5. This study shows that, together with ZTL, the ZTL homologs FKF1 and LKP2 are also involved in the same protein stability regulation to determine the pace and robustness of the plant circadian clock.
- Gibberellins Regulate Lateral Root Formation in Populus through Interactions with Auxin and Other Hormones
This work shows that gibberellins in poplar repress lateral root formation through interactions with other hormones like auxin. Gibberellin integrates aerial and root development, where aerial growth inhibition and concomitant stimulation of root proliferation produces a smaller plant with lower demands on environmental resources and a root system that can actively explore the soil environment.
- SOMBRERO, BEARSKIN1, and BEARSKIN2 Regulate Root Cap Maturation in Arabidopsis
This work demonstrates that three closely related Arabidopsis transcription factors are involved in activating the specific modifications to cell walls that are required for a fully functional root cap. These transcription factors share a generic transcriptional activity with other closely related proteins, which are involved in different aspects of cell wall modification.
- Apomictic and Sexual Ovules of Boechera Display Heterochronic Global Gene Expression Patterns
It is difficult for a purely mutational model to explain the evolution of asexuality in plants and animals. This work finds that expression patterns of many reproduction genes, including an overabundance of regulatory factors, differ during sexual and asexual ovule development, thus providing a possible mechanism for inducing the complex reproductive changes required to generate clonal offspring.
- Carbon Starved Anther Encodes a MYB Domain Protein That Regulates Sugar Partitioning Required for Rice Pollen Development
The authors identified a rice R2R3 MYB transcription factor, Carbon Starved Anther (CSA), that regulates sugar partitioning from leaves to anthers and is required for the production of functional pollen. CSA directly regulates the expression of the monosaccharide transporter gene MST8, which encodes a key component of the anther sugar unloading pathway.
- The Arabidopsis Floral Homeotic Proteins APETALA3 and PISTILLATA Negatively Regulate the BANQUO Genes Implicated in Light Signaling
This work provides evidence that APETALA3 and PISTILLATA influence petal morphogenesis in part through the negative regulation of a family of proteins that in turn modulate the activity of a number of other signaling pathways, providing a mechanistic link between developmental and physiological responses.
- SHORT HYPOCOTYL UNDER BLUE1 Truncations and Mutations Alter Its Association with a Signaling Protein Complex in Arabidopsis
Arabidopsis SHB1 contains two signature domains homologous to the SYG1 protein family from a variety of organisms and plant species, and the function of the two domains remains largely unknown. We report the function of the two signature domains of SHB1 in light signaling and the identification of an SHB1-containing light signaling complex in the nucleus.
- MGOUN1 Encodes an Arabidopsis Type IB DNA Topoisomerase Required in Stem Cell Regulation and to Maintain Developmentally Regulated Gene Silencing
This work examines the function of MGOUN1 (MGO1) in Arabidopsis stem cell maintenance, showing that mgo1 mutations enhance the specific stem cell defects in hypomorphic wuschel alleles. Positional cloning reveals that MGO1 encodes topoisomerase IB, thereby linking topoisomerase function to the propagation of developmentally regulated gene function.
- The Arabidopsis Stem Cell Factor POLTERGEIST Is Membrane Localized and Phospholipid Stimulated
This work explores how the shoot and root stem cell promoting factors POLTERGEIST (POL) and PLL1 are regulated at the cellular level. Specifically, this study reveals that both of these protein phosphatase type 2C proteins are membrane localized via acylation and that phospholipid binding stimulates POL activity.
- Spatial Configuration of Transposable Element Ac Termini Affects Their Ability to Induce Chromosomal Breakage in Maize
Chromosome breakage was the first property of transposable elements identified by McClintock. Evidence is presented to show that chromosome breakage can be attributed to alternative transposition reactions that involve the termini of multiple closely linked elements.
- Arabidopsis Homologs of Nucleus- and Phragmoplast-Localized Kinase 2 and 3 and Mitogen-Activated Protein Kinase 4 Are Essential for Microtubule Organization
Arabidopsis mutants defective in MAPK signaling were found to have aberrant microtubule organization and cell growth. This study shows that two mitogen-activated protein kinase kinase kinase isoforms, mitogen-activated protein kinase 4 and microtubule-associated protein 65, play a role in the organization of cortical microtubules.
- The Coiled-Coil Protein VIG1 Is Essential for Tethering Vacuoles to Mitochondria during Vacuole Inheritance of Cyanidioschyzon merolae
The mechanism of vacuole inheritance is poorly understood. This work makes use of the model organism C. merolae, which has a minimum set of organelles that are systematically inherited, and identifies vig1 as being essential for vacuole inheritance.
- bZIP28 and NF-Y Transcription Factors Are Activated by ER Stress and Assemble into a Transcriptional Complex to Regulate Stress Response Genes in Arabidopsis
This work provides evidence that both bZIP28 and NF-Y subunits are recruited under stress to form a transcriptional complex that upregulates the expression of endoplasmic reticulum stress-induced genes. The bZIP28/NF-Y complex specifically binds to an element common to the promoters of the targeted stress genes.
- Internal Architecture of Mitochondrial Complex I from Arabidopsis thaliana
The NADH dehydrogenase complex (complex I) represents the largest functional module of the respiratory chain and at the same time is the least known. Based on a novel biochemical strategy, a model on its internal structure is presented. In plants, complex I comprises several extra protein subunits that partially integrate side activities into the complex and contribute to its special shape.
- ANKYRIN REPEAT-CONTAINING PROTEIN 2A Is an Essential Molecular Chaperone for Peroxisomal Membrane-Bound ASCORBATE PEROXIDASE3 in Arabidopsis
ANKYRIN REPEAT-CONTAINING PROTEIN 2A (AKR2A) is known to be involved in targeting proteins to the chloroplast outer envelope membrane. This work provides evidence that AKR2A binds specifically to several single-membrane spanning proteins that are targeted to various cellular compartments, suggesting that AKR2A may serve as a molecular chaperone for a set of membrane proteins.
- RNAi Suppression of Arogenate Dehydratase1 Reveals That Phenylalanine Is Synthesized Predominantly via the Arogenate Pathway in Petunia Petals
This study analyzed the l-Phe biosynthetic pathways in Petunia hybrida flowers, which emit high levels of Phe-derived volatiles. RNA interference suppression of petunia arogenate dehydratase1 provides in planta evidence that l-Phe is synthesized via arogenate and uncovers a novel posttranscriptional regulation of the shikimate pathway.
- Genomic and Coexpression Analyses Predict Multiple Genes Involved in Triterpene Saponin Biosynthesis in Medicago truncatula
This study sought to identify genes involved in the biosynthesis of the triterpene skeleton in Medicago truncatula using a comprehensive gene expression clustering analysis. The UGT73F3 gene was shown to function as a uridine diphosphate glycosyltransferase in the biosynthesis of triterpene saponins.
- Alkylresorcinol Synthases Expressed in Sorghum bicolor Root Hairs Play an Essential Role in the Biosynthesis of the Allelopathic Benzoquinone Sorgoleone
Alkylresorcinol synthases (ARSs) are thought to participate in the biosynthesis of a diversity of defense-related plant phenolic lipids. This work presents the functional characterization of two ARS enzymes involved in the biosynthesis of allelochemicals produced in sorghum root hair cells as well as three enzymes likely dedicated to the biosynthesis of alkylresorcinolic phytoanticipins in rice.
- The Arabidopsis thaliana Myo-Inositol 1-Phosphate Synthase1 Gene Is Required for Myo-inositol Synthesis and Suppression of Cell Death
This work uses functional genomics to delineate the role of the inositol synthesis genes in regulating growth, development, and cell death and reveals a connection between inositol, phosphatidylinositol, and sphingolipids.
- High-Affinity Manganese Uptake by the Metal Transporter NRAMP1 Is Essential for Arabidopsis Growth in Low Manganese Conditions
This study shows that, in order to acquire manganese when concentrations in the soil are limited, Arabidopsis relies on a root high-affinity manganese uptake system catalyzed by the metal transporter NRAMP1. The finding that overexpression of NRAMP1 produces large plants with increased manganese content paves the way for the biotechnological engineering of plants with improved biomass production.
- Endosome-Associated CRT1 Functions Early in Resistance Gene–Mediated Defense Signaling in Arabidopsis and Tobacco
This work shows that the Arabidopsis CRT1 (for compromised for recognition of turnip crinkle virus) protein, a general resistance (R) protein-interacting protein, functions early in R gene–mediated defense responses. Moreover, reduction of the CRT1 family's activity compromises resistance to bacterial and oomycete pathogens and programmed cell death in Arabidopsis and Nicotiana benthamiana.
- Promoters of the Barley Germin-Like GER4 Gene Cluster Enable Strong Transgene Expression in Response to Pathogen Attack
The GER4 transcript encoding a germin-like protein of barley is derived from a dense cluster of tandemly duplicated, pathogen-induced genes that are subject to purifying selection. The GER4c promoter was found to regulate strong and pathogen-specific expression of the GUS reporter in barley, and multiple redundant WRKY factor binding sites were required for promoter activation.
- Common Genetic Pathways Regulate Organ-Specific Infection-Related Development in the Rice Blast Fungus
This study describes fungal infection–related development of Magnaporthe oryzae induced on rice roots and on hydrophilic polystyrene. A fungal mutant with abnormal preinfection hyphae and lacking the ortholog of the karyopherin exportin-5 had defects in full disease symptom production on leaves and roots, showing that this fungal karyopherin plays an important role during plant colonisation.
- Innate Immune Responses Activated in Arabidopsis Roots by Microbe-Associated Molecular Patterns
This study describes Arabidopsis root innate immune responses to various microbial elicitors and their salicylic acid signaling-independent suppression by coronatine, a phytotoxin produced by Pseudomonas syringae. These experiments have revealed new features of the root response to pathogen attack and the mechanisms that pathogens in turn may employ to block the host innate immune response.
