Table of Contents
IN BRIEF
LETTERS TO THE EDITOR
RESEARCH ARTICLES
- Chromosomal Phylogeny and Karyotype Evolution in x=7 Crucifer Species (Brassicaceae)
Karyotype evolution in eight species from six crucifer tribes has been reconstructed using comparative chromosome painting. The inferred chromosomal phylogeny provides compelling evidence for a monophyletic origin of the analyzed taxa from a common ancestral karyotype with seven chromosomes.
- Transcriptome-Wide Analysis of Uncapped mRNAs in Arabidopsis Reveals Regulation of mRNA Degradation
Uncapped mRNAs are important intermediates in mRNA degradation generated by decapping and cleavage by small RNAs and other endonucleases. The authors describe a versatile method for transcriptome-wide profiling of uncapped mRNA. Using this method, they provide evidence for widespread mRNA degradation control, which is associated with biological functions and gene structure features.
- Histone H2B Monoubiquitination in the Chromatin of FLOWERING LOCUS C Regulates Flowering Time in Arabidopsis
Histone H3 acetylation and methylation regulate FLOWERING LOCUS C (FLC) expression and, thus, flowering time. This work shows that histone H2B monoubiquitination, in the chromatin associated with the coding region of FLC and its homologs, is important for histone H3 methylation and their transcriptional activation.
- A Novel Class of Gibberellin 2-Oxidases Control Semidwarfism, Tillering, and Root Development in Rice
This work demonstrates how features of plant architecture, such as semidwarfism, increased root systems, and higher tiller numbers, might be improved to favor grain yield through manipulation of GA2ox expression.
- The Phytocalpain Defective Kernel 1 Is a Novel Arabidopsis Growth Regulator Whose Activity Is Regulated by Proteolytic Processing
The phytocalpain Defective Kernel 1 (DEK1) localizes to the plasma membrane and endomembranes. DEK1 undergoes autolytic cleavage releasing the cytoplasmic calpain domain. The active calpain domain alone is sufficient to rescue embryo-lethal dek1 mutants. Phenotypes associated with different levels of activity indicate that regulated DEK1 activity coordinates growth during organ development.
- NAC Family Proteins NARS1/NAC2 and NARS2/NAM in the Outer Integument Regulate Embryogenesis in Arabidopsis
Seed morphogenesis consists of embryogenesis and the development of maternal tissues such as the inner and outer integuments. This work shows that a deficiency of two NAC family proteins that are expressed in outer integuments but not in embryos causes a defect in embryogenesis. This result suggests that there is an intertissue communication between the embryo and the maternal integument.
- Root System Architecture in Arabidopsis Grown in Culture Is Regulated by Sucrose Uptake in the Aerial Tissues
This work shows that contact between the aerial tissues of the plant and the culture media can cause profound changes in root architecture and demonstrates that sucrose metabolism and ABA-dependent signaling are involved. These findings affect the interpretation of studies on root system architecture carried out in culture and also identify mechanisms of communication between above- and belowground tissues.
- IMPa-4, an Arabidopsis Importin α Isoform, Is Preferentially Involved in Agrobacterium-Mediated Plant Transformation
Agrobacterium transfers DNA and Virulence (Vir) proteins to plant cells. VirD2 and VirE2 interact with various members of the plant's importin (IMP) α protein family, which escort proteins to the nucleus. Genetic, biochemical, and imaging analyses indicate that IMPa-4 is the most crucial importin α isoform for transfer of bacterial Vir proteins to the plant nucleus.
- Abscisic Acid Coordinates Nod Factor and Cytokinin Signaling during the Regulation of Nodulation in Medicago truncatula
Nodulation in legumes is both dependent upon and regulated by plant hormones. This work shows that abscisic acid has multiple independent sites of action in the regulation of nodulation, regulating both Nod factor signaling in the epidermis and cytokinin-induced cell division in the cortex.
- EFD Is an ERF Transcription Factor Involved in the Control of Nodule Number and Differentiation in Medicago truncatula
This study reveals the role of EFD, a transcription factor belonging to the ERF family, in rhizobium-legume symbiotic interactions. EFD is involved both in the negative regulation of root nodule initiations and in the positive control of nodule differentiation. Based on the identification of an EFD target gene, these two roles are proposed to be mediated by the modulation of the cytokinin pathway.
- Isoprenylcysteine Methylation and Demethylation Regulate Abscisic Acid Signaling in Arabidopsis
Isoprenylcysteine methyltransferase is shown to be a negative regulator, and isoprenylcysteine methylesterase (ICME) a positive regulator, of ABA signaling in Arabidopsis thaliana. Moreover, ABA is shown to promote ABA responsiveness of plant cells via induction of ICME gene expression.
- The Gibberellic Acid Signaling Repressor RGL2 Inhibits Arabidopsis Seed Germination by Stimulating Abscisic Acid Synthesis and ABI5 Activity
This work studies the opposing effects of gibberellins (GAs) and abscisic acid (ABA) on seed germination through the transcription factors ABA-Insensitive5 (ABI5) and RGA-Like2 (RGL2). Low GA levels increase endogenous ABA in a RGL2-dependent manner, which induces ABI5, the final common repressor of germination in response to changes in ABA and GA levels.
- Conditional Repression of AUXIN BINDING PROTEIN1 Reveals That It Coordinates Cell Division and Cell Expansion during Postembryonic Shoot Development in Arabidopsis and Tobacco
The biological role of the putative receptor AUXIN BINDING PROTEIN1 (ABP1) in auxin signal perception has long been unclear. In this work, the authors use a variety of inducible suppression techniques to demonstrate that ABP1 is required for growth and cell division at various stages of plant development. These data define an essential function for ABP1 in the growing plant.
- A Battery of Transcription Factors Involved in the Regulation of Secondary Cell Wall Biosynthesis in Arabidopsis
This article demonstrates that eleven transcription factors are part of a transcriptional network that regulates secondary cell wall biosynthesis in Arabidopsis. SECONDARY WALL-ASSOCIATED NAC DOMAIN PROTEIN1, an established master switch of secondary cell wall biosynthesis, and its close functional homologs regulate the same downstream targets in different cell types.
- The Plant TPX2 Protein Regulates Prospindle Assembly before Nuclear Envelope Breakdown
Targeting Protein for Xklp2 (TPX2) is a central regulator of spindle assembly. This study characterizes plant TPX2 and demonstrates that it is actively exported from the nucleus before nuclear envelope breakdown. Thus, plants have adapted nuclear-cytoplasmic shuttling of TPX2 to maintain proper spindle assembly without centrosomes.
- F-Actin Organization and Pollen Tube Tip Growth in Arabidopsis Are Dependent on the Gametophyte-Specific Armadillo Repeat Protein ARO1
This study examines a small family of plant-specific Armadillo repeat proteins in Arabidopsis, of which one member, ARO1, shows gametophyte-specific expression and accumulates in the tips of pollen tubes. Genetic and functional data suggest that ARO1 is a novel player in maintaining polar growth of pollen tubes and in affecting the intracellular organization of the actin cytoskeleton.
- The Arabidopsis COP9 Signalosome Subunit 7 Is a Model PCI Domain Protein with Subdomains Involved in COP9 Signalosome Assembly
This work reports the crystallographic structure of the PCI domain of COP9 signalosome subunit 7 (CSN7) and finds that CSN7 is organized in three distinct physical and functional subdomains that mediate interaction with other COP9 signalosome subunits. The results point to a common structure-function thread that unifies the disparate multiprotein complexes in which PCI domains are found.
- Phytochrome A Regulates the Intracellular Distribution of Phototropin 1–Green Fluorescent Protein in Arabidopsis thaliana
Phototropism is the change in directional plant growth in response to light. This study shows that exposing an Arabidopsis plant to short pulses of red light before inducing phototropism by exposure to low fluence rates of blue light inhibits blue light–induced redistribution of the fluorescently tagged phototropin 1 photoreceptor. This inhibition may impact the plant's phototropic sensitivity.
- A Cytosolic Pathway for the Conversion of Hydroxypyruvate to Glycerate during Photorespiration in Arabidopsis
This article reports the identification of a cytosolic hydroxypyruvate reductase, HPR2, which provides an alternative to the peroxisomal hydroxypyruvate-to-glycerate conversion during photorespiration. Carbon partitioning between the peroxisomal and cytosolic pathways is probably regulated by the availability of NADH within the peroxisomes.
- NIP6;1 Is a Boric Acid Channel for Preferential Transport of Boron to Growing Shoot Tissues in Arabidopsis
Boron is an essential element for plants, and B transporters have been recently identified and characterized. This work shows that NIP6;1, a boric acid channel, is involved in preferential boron transport to young tissues in Arabidopsis shoots.
- Transgenic Arabidopsis Plants Expressing the Type 1 Inositol 5-Phosphatase Exhibit Increased Drought Tolerance and Altered Abscisic Acid Signaling
Transgenic plants expressing the human type I inositol 5-phosphatase have constitutively low basal InsP3 levels and increased drought tolerance. However, the levels of the drought-induced growth regulator, abscisic acid, remained lower in water-stressed transgenic plants. The results suggest that lowering InsP3 induced compensatory pathways that enhanced drought tolerance.
- Small Ubiquitin-Like Modifier Proteases OVERLY TOLERANT TO SALT1 and -2 Regulate Salt Stress Responses in Arabidopsis
Protein modification plays a critical role in plant responses to high salinity. An important form of such modifications is the attachment of a small polypeptide tag to a target protein. This study identifies two Arabidopsis nuclear proteases that regulate plant responses to high salinity by cleaving these polypeptide tags from their target proteins.
- The Arabidopsis onset of leaf death5 Mutation of Quinolinate Synthase Affects Nicotinamide Adenine Dinucleotide Biosynthesis and Causes Early Ageing
Leaf senescence is an age-dependent, genetically regulated process. Arabidopsis leaves can serve as a model system for studying the mechanisms and genetics of ageing. Here, it is shown that NAD influences the life span of Arabidopsis, suggesting a possible conserved role for NAD on development and ageing in plants and animals.
