Table of Contents
IN THIS ISSUE
IN BRIEF
RESEARCH ARTICLES
- Genetic and Epigenetic Alteration among Three Homoeologous Genes of a Class E MADS Box Gene in Hexaploid Wheat
Homoeologs are duplicated genes that arise from polyploidization. Bread wheat is hexaploid, with many triplicated homoeologs in the A, B, and D ancestral genomes. This work reports on both genetic and epigenetic alterations that have occurred in the homoeologs of a wheat class E MADS box gene that functions in floral organ identity and finds that only one of the three homoeologs is functional.
- Transcriptionally Active Heterochromatin in Rye B Chromosomes
A heterochromatic subterminal domain of a rye B chromosome with a unique combination of epigenetic marks undergoes decondensation during interphase and reveals substantial transcription of B-specific, high copy repeat families.
- Common Functions for Diverse Small RNAs of Land Plants
Some small RNAs are universally expressed in diverse land plants, while others are expressed only in certain lineages. This article presents the comprehensive discovery of microRNAs from the lycophyte Selaginella moellendorffii and the bryophyte Physcomitrella patens and demonstrates several instances where angiosperm and bryophyte small RNAs differing in sequence regulate similar targets.
- Suppression of RICE TELOMERE BINDING PROTEIN1 Results in Severe and Gradual Developmental Defects Accompanied by Genome Instability in Rice
Telomeres are nucleoprotein complexes essential for the integrity of eukaryotic chromosomes. This work examines the effects of RICE TELOMERE BINDING PROTEIN1 inactivation, silencing, and overexpression on telomere development. Mutant lines displayed progressive and severe developmental abnormalities in both vegetative and reproductive organs, accompanied by genome instability over four generations.
- The Triploid Endosperm Genome of Arabidopsis Adopts a Peculiar, Parental-Dosage-Dependent Chromatin Organization
In most flowering plants, the endosperm is a triploid nourishing tissue inheriting one paternal and two maternal genomes. This peculiar genetic constitution is accompanied by an atypical organization of the chromatin: endosperm nuclei contain interspersed heterochromatin associated with the H3K9me1 mark, which appears to be linked to dosage regulation of the parental genomes.
- Arabidopsis JAGGED LATERAL ORGANS Is Expressed in Boundaries and Coordinates KNOX and PIN Activity
Mutational analyses indicate that JAGGED LATERAL ORGANS (JLO) is first required for progression of embryogenesis beyond the globular stage and later is expressed in boundaries. JLO activates KNOX gene expression but represses PIN1. This work suggests that JLO acts from the boundary to orchestrate the drastic changes in gene expression that entail the initiation of plant lateral organs.
- BLADE-ON-PETIOLE1 and 2 Control Arabidopsis Lateral Organ Fate through Regulation of LOB Domain and Adaxial-Abaxial Polarity Genes
Plant lateral organ fate specification involves intersecting regulatory pathways. The BLADE-ON-PETIOLE1 (BOP1) and BOP2 genes promote Arabidopsis organ cell fate by upregulating LOB domain genes and downregulating class I knox genes. BOP1 and BOP2 also act redundantly with AS1 and AS2 to specify adaxial leaf petiole polarity by controlling lateral organ polarity gene expression.
- Mutations in Arabidopsis Multidrug Resistance-Like ABC Transporters Separate the Roles of Acropetal and Basipetal Auxin Transport in Lateral Root Development
Multidrug resistance (MDR)-like ABC transporters function in auxin transport and may contribute to root system development. Mutations that selectively disrupt one or the other of two distinct auxin streams show that lateral root primordia develop normally when MDR1-dependent delivery of auxin is abolished, but subsequent lateral root elongation depends strongly on MDR1-dependent auxin flow.
- Separating the Roles of Acropetal and Basipetal Auxin Transport on Gravitropism with Mutations in Two Arabidopsis Multidrug Resistance-Like ABC Transporter Genes
MDR1 and MDR4 ABC transporters are shown to mediate acropetal and basipetal auxin transport, respectively. High-resolution computer vision tools show that straight growth control but not gravitropism of roots depends on acropetal transport. Impaired basipetal transport does not affect straight growth but alters gravity-induced auxin asymmetry and subsequent development of gravitropic curvature.
- Inactivation of Thioredoxin Reductases Reveals a Complex Interplay between Thioredoxin and Glutathione Pathways in Arabidopsis Development
Thioredoxin reductases determine the redox state of the thioredoxin reducing system. This study defines an alternative reduction pathway of cytosolic thioredoxin that involves the glutathione/glutaredoxin pathway. A genetic approach shows that at least one of either the thioredoxin reductase/thioredoxin or glutathione/glutaredoxin pathways is required for postembryonic apical meristem activity.
- Reciprocal Phosphorylation and Glycosylation Recognition Motifs Control NCAPP1 Interaction with Pumpkin Phloem Proteins and Their Cell-to-Cell Movement
Plants use plasmodesmata (PD) for the cell-to-cell trafficking of proteins, and this process appears to involve receptors that target these proteins to the entry of the PD. This study demonstrates that phosphorylation and glycosylation of residues on both NCAPP1, a PD receptor, and Cm-PP16, a non-cell-autonomous phloem protein, controls their interaction leading to Cm-PP16 trafficking.
- INCREASED SIZE EXCLUSION LIMIT2 Encodes a Putative DEVH Box RNA Helicase Involved in Plasmodesmata Function during Arabidopsis Embryogenesis
This research characterizes an Arabidopsis embryo-defective mutant ise2 affecting plasmodesmata structure and function. ISE2 encodes a putative RNA helicase that localizes to cytoplasmic stress granules. ISE2 is required for posttranscriptional gene silencing and cell fate determination and regulates plasmodesmata architecture and aperture during embryogenesis.
- Ubiquitin Lysine 63 Chain–Forming Ligases Regulate Apical Dominance in Arabidopsis
Ubiquitin chains linked via Lys-63 play an important role in animal signaling cascades. This work demonstrates that ubiquitin ligases RGLG1 and RGLG2 of Arabidopsis can form such chains and localize to the plasma membrane. Loss of function led to changes in plant architecture that were linked to changes in auxin transport.
- SDIR1 Is a RING Finger E3 Ligase That Positively Regulates Stress-Responsive Abscisic Acid Signaling in Arabidopsis
Ubiquitination plays important roles in the perception and signal transduction of various internal and external environmental signals. This study reveals that the RING finger protein SALT AND DROUGHT INDUCED RING FINGER1 is an E3 ubiquitin ligase that is involved in salt and drought stress and ABA signaling and is a positive regulator of ABA signal transduction.
- ACTIN BINDING PROTEIN29 from Lilium Pollen Plays an Important Role in Dynamic Actin Remodeling
Lilium ACTIN BINDING PROTEIN29 (ABP29) from lily pollen is a Ca2+-dependent actin filament–severing protein belonging to the villin/gelsolin/fragmin superfamily. This work demonstrates that ABP29 is a splicing variant of Lilium villin and that it plays an important role in dynamic actin remodeling, especially in the processes of pollen germination and tube growth.
- Structural Evidence for the Evolution of Xyloglucanase Activity from Xyloglucan Endo-Transglycosylases: Biological Implications for Cell Wall Metabolism
Three-dimensional structures of the archetypal glycoside hydrolase family 16 (GH16) endo-xyloglucanases NXG1 and NXG2 from nasturtium were solved by x-ray crystallography. These structures, along with comparative biochemical and phylogenetic analyses, highlight important structure-function relationships in the family of GH16 enzymes, which are responsible for xyloglucan modification in the cell wall.
- In Vivo Visualization of Mg-ProtoporphyrinIX, a Coordinator of Photosynthetic Gene Expression in the Nucleus and the Chloroplast
In the plant cell, the genetic information is divided among three compartments, the nucleus, mitochondria, and chloroplasts. The activities of these three genomes must be coordinated. Through retrograde communication, the organelles emit signals that regulate the nuclear genes. One of the plastid signals, Mg-ProtoIX was found to control the expression of both nuclear- and plastid-encoded photosynthesis genes.
- Retracted: LPA2 Is Required for Efficient Assembly of Photosystem II in Arabidopsis thaliana
Biogenesis and assembly of photosystem II is mainly regulated by nuclear-encoded factors. This work reports the identification of a nuclear-encoded factor LPA2 that is involved in efficient photosystem II assembly, probably through direct interaction with photosystem II core protein CP43.
- Rational Conversion of Substrate and Product Specificity in a Salvia Monoterpene Synthase: Structural Insights into the Evolution of Terpene Synthase Function
Terpene synthases are central in the biosynthesis of the complex chemical arsenal of plants. This article reports the high-resolution three-dimensional structure of 1,8-cineole synthase from Salvia fruticosa, defines the active residues and their roles in catalysis, and demonstrates how the active site can be engineered to generate other monoterpene and larger sesquiterpene products.
- A Heteromeric Plastidic Pyruvate Kinase Complex Involved in Seed Oil Biosynthesis in Arabidopsis
Oil biosynthesis in green embryos requires carbon precursors derived from glycolysis. A multifaceted analysis suggests that at least 60% of carbon entering fatty acid synthesis depends on a plastidic pyruvate kinase complex. This work underscores the role of metabolic compartmentation in controlling carbon partitioning in developing seeds and provides new avenues for the engineering of seed oil.
- The Arabidopsis MATE Transporter TT12 Acts as a Vacuolar Flavonoid/H+-Antiporter Active in Proanthocyanidin-Accumulating Cells of the Seed Coat
Flavonoid biosynthesis is one of the best-characterized pathways, yet transporters required for vacuolar storage or secretion are still largely unknown. The characterization of the Arabidopsis tt12 mutant suggested that the MATE protein TT12 is involved in flavonoid deposition in seeds. TT12 localizes to the tonoplast and mediates H+-coupled transport of selected glucosylated flavonoids.
- Arabidopsis Cytochrome P450 Monooxygenase 71A13 Catalyzes the Conversion of Indole-3-Acetaldoxime in Camalexin Synthesis
Phytoalexins are small antimicrobial compounds produced by plants in response to pathogen attack. Camalexin (3-thiazol-2-yl-indole) is an indole alkaloid phytoalexin in Arabidopsis important for resistance to necrotrophic fungal pathogens. This work demonstrates the involvement of the CYP71A13 enzyme in camalexin biosynthesis and pathogen resistance.
- Suppression of Antiviral Silencing by Cucumber Mosaic Virus 2b Protein in Arabidopsis Is Associated with Drastically Reduced Accumulation of Three Classes of Viral Small Interfering RNAs
Viral protein 2b facilitates systemic infection by suppressing non-cell-autonomous RNA silencing. This work identifies a major role for host RNA-dependent RNA polymerase 1 in the biogenesis of viral siRNAs and shows that 2b expression inhibits accumulation of all classes of viral siRNAs in infected plants, thus illustrating how viruses may suppress non-cell-autonomous antiviral silencing.
- Rice WRKY45 Plays a Crucial Role in Benzothiadiazole-Inducible Blast Resistance
Genetic and biochemical analyses demonstrate that rice WRKY45 is a transcriptional activator that acts in the SA signaling pathway to mediate defense signaling.
- Bacterial Cyclic β-(1,2)-Glucan Acts in Systemic Suppression of Plant Immune Responses
Analysis of a bacterial black rot mutant that fails to synthesize extracellular cyclic β-(1,2)-glucan and its effects in the model plants Arabidopsis thaliana and Nicotiana benthamiana shows that this cyclic glucan functions in pathogen virulence and supports the idea that systemic suppression of induced plant defenses is a counterdefensive strategy that facilitates pathogen spread in plants.
