Table of Contents
IN BRIEF
PERSPECTIVE
RESEARCH ARTICLES
- Structural and Functional Divergence of a 1-Mb Duplicated Region in the Soybean (Glycine max) Genome and Comparison to an Orthologous Region from Phaseolus vulgaris
Comparative analysis of homoeologous regions in soybean (Glycine max) and an orthologous region from common bean (Phaseolus vulgaris) reveal asymmetric evolution between homoeologous regions of soybean as evidenced by structural and gene expression changes. These results shed light on the fate of duplicated genes and chromosome segments after a whole-genome duplication in a paleopolyploid plant.
- Hidden Variability of Floral Homeotic B Genes in Solanaceae Provides a Molecular Basis for the Evolution of Novel Functions
This study examines the evolution of a duplicate regulatory system in a tobacco species and tomato. Although individual B-class genes have various functions, the overall role of these genes is to specify petal and stamen identities. Transformed organs transition into an adjacent whorl by fusion, and in response additional organs develop of which the identity is different between species.
- Finite Element Model of Polar Growth in Pollen Tubes
The generation of different shapes in plant cells depends on the spatial regulation of the cell wall mechanical properties. A finite element modeling approach was used to simulate the unidirectional growth process in pollen tubes. Predictions made by the model suggest a crucial role for the chemical configuration of pectin in determining cell shape.
- Phosphoenolpyruvate Provision to Plastids Is Essential for Gametophyte and Sporophyte Development in Arabidopsis thaliana
This work examines double mutants defective in providing phosphoenolpyruvate (PEP) to the plastids and finds that PEP is essential for multiple steps in plant development, reflecting the central importance of PEP in multiple plant metabolic pathways, including synthesis of aromatic amino acids, lipids, flavonoids, and lignin.
- TDIF Peptide Signaling Regulates Vascular Stem Cell Proliferation via the WOX4 Homeobox Gene in Arabidopsis
This study shows that the TDIF signal from the phloem plays a crucial role in the maintenance of vascular stem cells via two independent pathways: WOX4-independent inhibition of xylem commitment of vascular stem cells and WOX4-mediated enhancement of their proliferation.
- Abscisic Acid Increases Arabidopsis ABI5 Transcription Factor Levels by Promoting KEG E3 Ligase Self-Ubiquitination and Proteasomal Degradation
This work shows that KEG E3 ligase activity is required for regulation of the abundance of the ABA responsive transcription factor ABI5. It shows that KEG undergoes autoubiquitination in response to ABA and is degraded by the 26S proteasome, allowing ABI5 levels to increase and mediate cellular ABA responses.
- Nonspecific Phospholipase C NPC4 Promotes Responses to Abscisic Acid and Tolerance to Hyperosmotic Stress in Arabidopsis
Elimination of Arabidopsis nonspecific phospholipase C (NPC4) results in decreases in diacylglycerol levels, abscisic acid (ABA) sensitivity, and hyperosmotic stress tolerance, whereas overexpression of NPC4 has opposite effects. This indicates that NPC4 promotes ABA response under hyperosmotic stress, whereas NPC-derived diacylglycerol enhances stomatal opening under well-watered conditions.
- Perturbation of Indole-3-Butyric Acid Homeostasis by the UDP-Glucosyltransferase UGT74E2 Modulates Arabidopsis Architecture and Water Stress Tolerance
The hydrogen peroxide–responsive UDP-glucosyltransferase UGT74E2 from Arabidopsis thaliana is shown to be involved in modulation of plant architecture and water stress response through its activity toward the auxin indole-3-butyric acid (IBA). Evidence is provided that, during water stress, IBA and IBA-glucose levels increase, and auxins help maintain the photosynthetic capacity under stress.
- Characterization of the Molecular Mechanism Underlying Gibberellin Perception Complex Formation in Rice
DELLA degradation, a key event in gibberellin (GA) signaling, is triggered by the GA-dependent interaction between the GA receptor GID1 and the DELLA/TVHYNP motif of DELLA. The interaction between GID1 and the DELLA/TVHYNP motif is found to enable the C-terminal GRAS domain of DELLA to interact with GID1, which leads to the degradation of the DELLA protein SLR1 via the SCFGID2 E3 ligase.
- The Conserved RNA Trafficking Proteins HPR1 and TEX1 Are Involved in the Production of Endogenous and Exogenous Small Interfering RNA in Arabidopsis
This work uses a forward genetic screen to identify mutants defective in postranscriptional gene silencing (PTGS), finding components required in multiple PTGS pathways or required only in specific PTGS pathways.
- The Type II Arabidopsis Formin14 Interacts with Microtubules and Microfilaments to Regulate Cell Division
Formins primarily have been shown to associate with, and regulate the dynamics of, microfilaments. This work shows that AFH14, a formin from Arabidopsis thaliana, regulates both microtubule and microfilament arrays in vitro and in vivo and plays important roles in mitosis and meiosis in plant cells.
- Arabidopsis VILLIN1 and VILLIN3 Have Overlapping and Distinct Activities in Actin Bundle Formation and Turnover
Villins are a class of actin-binding protein with multiple activities. This study uses single filament imaging techniques to evaluate and contrast the functions of Arabidopsis VILLIN1 (VLN1) and VLN3. Both isovariants are shown to bundle actin filaments, whereas VLN3 also severs filaments and can disassemble actin filament bundles in the presence of physiological calcium concentrations.
- Arabidopsis VILLIN5, an Actin Filament Bundling and Severing Protein, Is Necessary for Normal Pollen Tube Growth
Villin is a major regulator of actin dynamics. This article reports that Arabidopsis thaliana VILLIN5 (VLN5) is a typical member of the villin/gelsolin/framin family and retains a full suite of activities in vitro, including capping, severing, and bundling of actin filaments. Moreover, using reverse genetics, we show that VLN5 is required for the stabilization of actin filaments in the pollen tube.
- Dysfunction of Chromatin Assembly Factor 1 Induces Shortening of Telomeres and Loss of 45S rDNA in Arabidopsis thaliana
Replication-dependent chromatin assembly contributes to the stability of the copy number of the telomeric and 45S rDNA repeats. While only 10 to 20% of the 45S rDNA repeats remain intact in the 5th generation of the CAF1 mutants, transcription is unaltered. The progressive loss of telomeres and 45S rDNA is accompanied by accumulation of anaphase bridges and increased sterility of the plants.
- Tobacco GTBP1, a Homolog of Human Heterogeneous Nuclear Ribonucleoprotein, Protects Telomeres from Aberrant Homologous Recombination
Telomeres are essential for the integrity of linear eukaryotic chromosomes. This study provides evidence that GTBP1, a single-strand telomere binding protein, is an essential component for telomere structure and function in tobacco by preventing aberrant interchromosomal telomeric homologous recombination.
- PHOSPHATIDIC ACID PHOSPHOHYDROLASE1 and 2 Regulate Phospholipid Synthesis at the Endoplasmic Reticulum in Arabidopsis
Regulation of membrane biogenesis is important for cell function. In this article, two phosphatic acid phosphohydrolase enzymes from Arabidopsis are characterized, and it is shown that their disruption leads to activation of phospholipid synthesis and altered endoplasmic reticulum membrane morphology. The data suggest that either the enzymes or their substrate/product regulate endoplasmic reticulum membrane biogenesis.
- The AP-3 β Adaptin Mediates the Biogenesis and Function of Lytic Vacuoles in Arabidopsis
A fluorescence imaging–based forward genetic screen for Arabidopsis mutants displaying abnormal intracellular distribution of the plasma membrane–localized auxin efflux carrier PIN1-GFP identifies PAT2, coding for a putative AP-3 β adaptin. pat2 is defective in biogenesis, morphology, and identity of lytic vacuoles, resulting in defective degradation and vacuolar accumulation of proteins.
- The Cytosolic Tail Dipeptide Ile-Met of the Pea Receptor BP80 Is Required for Recycling from the Prevacuole and for Endocytosis
We analyzed trafficking features of the vacuolar sorting receptor BP80, identified a dipeptide retrieval signal Ile-Met, and demonstrated that BP80 undergoes brefeldin A–sensitive endocytic cycling. Ile-Met plays a dual role (1) in the main pathway by preventing the receptor to follow its ligand towards the lytic vacuole and (2) in the alternative route by participating in the receptor endocytosis.
- Y3IP1, a Nucleus-Encoded Thylakoid Protein, Cooperates with the Plastid-Encoded Ycf3 Protein in Photosystem I Assembly of Tobacco and Arabidopsis
Ycf3 is a plastid-encoded gene known to function in the assembly of photosystem I (PSI). This study revealed that Ycf3-interacting protein 1, a nucleus-encoded thylakoid protein, interacts with Ycf3 to promote the assembly of PSI units in the thylakoid membrane.
- Functional Differentiation of the Glycosyltransferases That Contribute to the Chemical Diversity of Bioactive Flavonol Glycosides in Grapevines (Vitis vinifera)
This article identifies two previously unknown flavonol glycosyltransferases of grapevines and compares them in terms of sugar donor specificity. These enzymes are considered paralogous, and a scenario for evolution of new sugar donor specificity of glycosyltransferases is proposed based on the results of phylogenetic, biochemical, and molecular modeling studies of these enzymes.
- Network Analysis of Enzyme Activities and Metabolite Levels and Their Relationship to Biomass in a Large Panel of Arabidopsis Accessions
This work uses natural genetic diversity to study species-wide connectivity between metabolites, enzymes, and biomass. The resulting network analysis, based on 129 Arabidopsis accessions, shows that biomass can be predicted by two independent integrative metabolic biomarkers: preferential investment in photosynthetic machinery and optimization of carbon use.
- Redox Regulation of the NPR1-TGA1 System of Arabidopsis thaliana by Nitric Oxide
Nitric oxide (NO) regulates many physiological processes in plants. This research demonstrates that NO acts as a redox regulator of a transcription factor network that is a key component of plant defense and systemic acquired resistance. Specifically, NO modifies the NPR1 and TGA1 transcription factors by S-nitrosylating critical amino acids, resulting in enhanced transcription of defense genes.
- The Ustilago maydis Clp1 Protein Orchestrates Pheromone and b-Dependent Signaling Pathways to Coordinate the Cell Cycle and Pathogenic Development
In the fungus Ustilago maydis, the ability to infect plants and the coordination of the cell cycle are closely interconnected. This work shows that a protein (Clp1) physically interacts with two master regulatory proteins (bW and Rbf1) that are both essential for pathogenic development and alters their function to coordinate infection and the cell cycle.
COMMENTARY