Table of Contents
EDITORIAL
IN BRIEF
LETTERS TO THE EDITOR
RESEARCH ARTICLES
- Arabidopsis Relatives of the Human Lysine-Specific Demethylase1 Repress the Expression of FWA and FLOWERING LOCUS C and Thus Promote the Floral Transition
Genetic and biochemical analyses show that the histone H3-Lys 4 demethylases LDL1 and LDL2 reduce the levels of methylation and repress expression of the floral repressors FLC and FWA. Repression of FWA was associated with affects on DNA methylation, whereas FLC repression was not, suggesting that members of the LDL family can participate in a range of silencing mechanisms.
- A Circadian Rhythm Set by Dusk Determines the Expression of FT Homologs and the Short-Day Photoperiodic Flowering Response in Pharbitis
Different plant species flower in response to long days or short days (SDs), and this difference evolved several times. The SD response of Pharbitis is shown to be controlled by a different mechanism than those described for Arabidopsis and rice. In Pharbitis, a circadian clock set by dusk regulates transcription of the flowering-time gene FT.
- MPB2C, a Microtubule-Associated Protein, Regulates Non-Cell-Autonomy of the Homeodomain Protein KNOTTED1
The study shows that the microtubule-associated and viral movement protein binding protein MPB2C homologs from Arabidopsis and Nicotiana interact with homeodomain proteins KN1 and STM but not with BEL1. MPB2C proteins alter the subcellular distribution of KN1/STM and negatively regulate KN1 cell-to-cell transport.
- Two Calcium-Dependent Protein Kinases, CPK4 and CPK11, Regulate Abscisic Acid Signal Transduction in Arabidopsis
This work shows that CPK4 and CPK11 are positive regulators in the CDPK/calcium-mediated abscisic acid signaling pathways and that the transcription factors ABF1 and ABF4 are substrates of both kinases.
- Global Analysis of DELLA Direct Targets in Early Gibberellin Signaling in Arabidopsis
DELLA proteins restrict plant growth by inhibiting responses to the plant hormone gibberellin. From the data presented in this study, these proteins appear to activate the expression of downstream transcription factors, which are likely to function as negative regulators of gibberellin signaling.
- The GID1-Mediated Gibberellin Perception Mechanism Is Conserved in the Lycophyte Selaginella moellendorffii but Not in the Bryophyte Physcomitrella patens
The presence of genes encoding functional GA signaling– and GA synthesis–related proteins, such as GID1, DELLAs, F-box proteins, GA20 oxidase, and GA3 oxidase in Selaginella moellendorffii, suggests conserved GA perception and synthesis mechanisms among vascular plants. By contrast, equivalent functional genes were not found in the bryophyte Physcomitrella patens.
- Differential Requirements for RAD51 in Physcomitrella patens and Arabidopsis thaliana Development and DNA Damage Repair
This work shows that homologous recombination dependent on RAD51 is used for somatic DNA damage repair in P. patens, but not in Arabidopsis, implying fundamental differences in the use of recombination pathways between these species and suggesting that the choice of recombination pathway is related to the speed of evolution in plants.
- The Catalytically Active Tyrosine Residues of Both SPO11-1 and SPO11-2 Are Required for Meiotic Double-Strand Break Induction in Arabidopsis
In contrast with other eukaryotes, plants need two functional SPO11 homologs for double-strand break induction initiating meiotic recombination. A mutation in the catalytic center of either protein prevents double-strand break formation and leads to male and female sterility and unbalanced chromosome segregation.
- MIDGET Unravels Functions of the Arabidopsis Topoisomerase VI Complex in DNA Endoreduplication, Chromatin Condensation, and Transcriptional Silencing
MIDGET was identified as a new functional component of the plant DNA topoisomerase VI complex. This work shows that MIDGET, in addition to having a known function in endoreduplication, is involved in chromatin organization, transcriptional silencing, and ATR-dependent DNA damage repair checkpoint activation.
- Class-Specific Interaction of Profilin and ADF Isovariants with Actin in the Regulation of Plant Development
This work examines the functionally distinct interactions among major classes of actins and actin binding proteins (ABPs) in vivo and shows that actin and ABP isovariants have evolved class-specific protein–protein interactions that are essential to the normal regulation of plant growth and development.
- Subcellular Localization and Functional Domain Studies of DEFECTIVE KERNEL1 in Maize and Arabidopsis Suggest a Model for Aleurone Cell Fate Specification Involving CRINKLY4 and SUPERNUMERARY ALEURONE LAYER1
Aleurone cells, the epidermal cell layer of the maize endosperm, differentiate in response to surface position via a process that depends on DEK1, CR4, and SAL1. DEK1 and CR4 colocalize at the plasma membrane and in endosomes together with SAL1. The model presented for aleurone cell fate specification is proposed to represent a global model for plant epidermal cell fate specification.
- Arabidopsis Cryptochrome 2 Completes Its Posttranslational Life Cycle in the Nucleus
The Arabidopsis blue light receptor CRY2 mediates blue light inhibition of hypocotyl elongation and photoperiodic regulation of floral initiation. This study shows that CRY2 exerts those two functions in the nucleus; CRY2 is phosphorylated in the nucleus, and it is ubiquitinated and degraded by the ubiquitination/26S proteasome pathway in the nucleus.
- Arabidopsis Cotyledon-Specific Chloroplast Biogenesis Factor CYO1 Is a Protein Disulfide Isomerase
Chloroplast biogenesis programs differ in cotyledons and true leaves. Here, Arabidopsis mutant analysis shows that CYO1 acts specifically in the light-dependent conversion of cotyledon etioplasts to chloroplasts. CYO1 is tightly associated with thylakoids and catalyzes disulfide bond rearrangements, suggesting that it has a chaperone-related function required for thylakoid biogenesis in cotyledeons.
- Proteome Analysis of Arabidopsis Leaf Peroxisomes Reveals Novel Targeting Peptides, Metabolic Pathways, and Defense Mechanisms
The development of a new isolation protocol for leaf peroxisomes from Arabidopsis enabled a comprehensive proteome analysis that led not only to the recognition of newfound, plant-specific metabolic pathways and defense mechanisms, but also to the characterization of novel targeting peptides, an extended definition of PTS2 domains, and the proposal of alternative protein import pathways.
- Manipulation of Phytoene Levels in Tomato Fruit: Effects on Isoprenoids, Plastids, and Intermediary Metabolism
Altering pigment formation in tomato fruit by genetic manipulation has shown that different aspects of fruit ripening are regulated separately. Carotenoid formation is not correlated to other fruit ripening parameters, such as ethylene production, increased sweetness, and fruit softening.
- Evolution of Cinnamate/p-Coumarate Carboxyl Methyltransferases and Their Role in the Biosynthesis of Methylcinnamate
Gene expression, enzyme activity, and metabolite analyses show that CCMTs catalyze methylcinnamate formation in sweet basil. Phylogenetic analysis places CCMTs in a clade with many uncharacterized carboxyl methyltransferase–like proteins from monocots and more primitive plants. Structural modeling and site-directed mutagenesis identify active site residues contributing to CCMT substrate specificity.
- Enhanced Thermostability of Arabidopsis Rubisco Activase Improves Photosynthesis and Growth Rates under Moderate Heat Stress
Rubisco activase is a thermolabile enzyme that loses the ability to activate Rubisco at elevated temperatures. Therefore, photosynthesis is inhibited under moderately elevated temperatures. Arabidopsis Rubisco activase deletion mutant expressing thermostable variants generated by gene shuffling exhibited positive impact on photosynthesis, growth, and yield under moderate heat stress conditions.
- SALT TOLERANCE HOMOLOG2, a B-Box Protein in Arabidopsis That Activates Transcription and Positively Regulates Light-Mediated Development
SALT TOLERANCE HOMOLOG2 (STH2) is identified as a gene that interacts genetically with two key regulators of light signaling, HY5 and COP1. Results indicate that the B-box–containing protein STH2 acts as a positive regulator of photomorphogenesis and that the B-box domain plays a direct role in activating transcription in plants.
- The Pentatricopeptide Repeat Gene OTP43 Is Required for trans-Splicing of the Mitochondrial nad1 Intron 1 in Arabidopsis thaliana
Mutant Arabidopsis plants with a disrupted OTP43 gene have undetectable mitochondrial Complex I activity and show severe defects in seed development, germination, and to a lesser extent in plant growth.
- The Arabidopsis Mitogen-Activated Protein Kinase Kinase MKK3 Is Upstream of Group C Mitogen-Activated Protein Kinases and Participates in Pathogen Signaling
This work shows that the MKK3 pathway plays a role in pathogen defense. MKK3 is induced by pathogen infection but not by abiotic stress, and growth of virulent Pseudomonas syringae was enhanced in mkk3 knockout plants and inhibited in MKK3-overexpressing plants. Further experiments showed that MKK3 is an activator of group C MAP kinases and acts to induce the expression of several PR genes.
- Polar Growth in the Infectious Hyphae of the Phytopathogen Ustilago maydis Depends on a Virulence-Specific Cyclin
Formation of polarized hyphae in plant pathogenic fungi may limit fungal invasion of the plant tissue. This work shows that pcl12, encoding a Cdk5-interacting cyclin, represents a polarity and virulence regulator in the corn smut fungus Ustilago maydis. The results support the conclusion that fungal morphogenesis is a component of fungal host invasion capacity.
- Identification and Mutational Analysis of Arabidopsis FLS2 Leucine-Rich Repeat Domain Residues That Contribute to Flagellin Perception
A method to study structure–function relationships within the diverse and biologically important family of leucine-rich repeat (LRR) domains was developed and used to study Arabidopsis FLAGELLIN SENSING2 (FLS2). A small region was identified within the LRR of FLS2 that is involved in flagellin perception, within which mutations abolish flagellin binding and prevent downstream defense elicitation.
