Table of Contents
IN BRIEF
RESEARCH ARTICLES
- Dynamic Evolution of Oryza Genomes Is Revealed by Comparative Genomic Analysis of a Genus-Wide Vertical Data Set
This work combines a phylogenetic framework of closely related Oryza species with a large-scale comparative sequence sampling from every phylogenetic branch from a single orthologous Adh1-Adh2 genomic region. It details a chronological series of evolutionary events, their pace, mechanistic causes, and impact on genome evolution in this genus that occurred within a 15-million-year time period.
- Functional Proteomics of Arabidopsis thaliana Guard Cells Uncovers New Stomatal Signaling Pathways
This study identifies 1734 proteins of the guard cell proteome, examines novel signaling pathways, and finds that a myrosinase implicated in plant–herbivore interactions, THIOGLUCOSIDE GLUCOHYDROLASE1 (TGG1), is abundant in guard cells. Mutant analysis reveals key roles of TGG1 in ABA regulation of K+ channels and stomatal apertures, suggesting interplay between biotic and abiotic signaling.
- Proteomic Identification and Characterization of a Novel Peroxisomal Adenine Nucleotide Transporter Supplying ATP for Fatty Acid β-Oxidation in Soybean and Arabidopsis
This work identifies a novel protein, Glycine max PEROXISOMAL ADENINE NUCLEOTIDE CARRIER (PNC1), by proteomic analyses of peroxisomal membrane proteins. PNC1 and its homologs in Arabidopsis contribute to the transport of adenine nucleotides that are consumed by reactions to generate acyl-CoA for peroxisomal fatty acid β-oxidation during postgerminative growth.
- Peroxisomal ATP Import Is Essential for Seedling Development in Arabidopsis thaliana
This study shows that plant peroxisomes depend on ATP import from the cytosol to drive ATP-dependent reactions in the peroxisomal matrix. Two redundant ATP carriers that mediate an exchange of ATP with AMP or ADP across the peroxisomal membrane catalyze the import of ATP.
- Phosphate Availability Alters Lateral Root Development in Arabidopsis by Modulating Auxin Sensitivity via a Mechanism Involving the TIR1 Auxin Receptor
Lateral root formation is stimulated in plants deprived of phosphate. Here, phosphate-deprived Arabidopsis seedlings are shown to have an increased sensitivity to auxin, which alters the expression of auxin-responsive genes and promotes lateral root formation.
- A Tobacco Calcium-Dependent Protein Kinase, CDPK1, Regulates the Transcription Factor REPRESSION OF SHOOT GROWTH in Response to Gibberellins
REPRESSION OF SHOOT GROWTH (RSG) is a transcriptional activator functioning in GA feedback by regulating GA biosynthetic enzymes. This work identified a Ca2+-dependent protein kinase that regulates RSG by phosphorylation of RSG residue Ser-114. These results suggest that CDPK decodes the Ca2+ signal produced by GAs and regulates the intracellular localization of RSG.
- Characterization of the Arabidopsis Nitrate Transporter NRT1.6 Reveals a Role of Nitrate in Early Embryo Development
This study of the nitrate transporter NRT1.6, which is expressed in the funiculus, showed that nitrate is important for early embryo development. In the nrt1.6 mutants, abnormalities were found mainly in the suspensor cells at the one- or two-cell stages of embryo development.
- Truncation of a Protein Disulfide Isomerase, PDIL2-1, Delays Embryo Sac Maturation and Disrupts Pollen Tube Guidance in Arabidopsis thaliana
The authors show that Arabidopsis PDIL2-1 is a functional protein disulfide isomerase localized in the ER and highly expressed in the micropylar region of the ovule. They also show that gain-of-function mutations, caused by truncated versions of enzymatically active PDIL2-1, act in sporophytic tissues. These mutations delay embryo sac maturation and disrupt pollen tube guidance in Arabidopsis.
- Type B Phosphatidylinositol-4-Phosphate 5-Kinases Mediate Arabidopsis and Nicotiana tabacum Pollen Tube Growth by Regulating Apical Pectin Secretion
PtdIns(4,5)P2 is enriched in the tip plasma membrane of pollen tubes. Its functions in pollen tubes are unclear, as PtdIns(4,5)P2 biosynthetic enzymes are poorly characterized. Two pollen-expressed PI4P 5-kinases were found to be required for normal germination and growth of pollen tubes, and overexpression phenotypes indicated that PtdIns(4,5)P2 has effects on pectin secretion at the growing apex.
- Characterization of Raphanus sativus Pentatricopeptide Repeat Proteins Encoded by the Fertility Restorer Locus for Ogura Cytoplasmic Male Sterility
The Rfo locus restores fertility to radish plants with Ogura cytoplasmic male sterility. Using transgenic rapeseed plants expressing genes of this locus, this study shows that the product of one gene associates in vivo with the sterility gene RNA and restores fertility by suppressing the synthesis of the sterility protein in the tapetum of anthers.
- The C-Terminal Variable Region Specifies the Dynamic Properties of Arabidopsis Microtubule-Associated Protein MAP65 Isotypes
The organization of microtubule arrays in plant cell morphogenesis depends on proteins that bundle microtubules. The major bundling protein is MAP65, which is encoded by a gene family comprising different isotypes that have unique abilities important for cell cycle progression. This work shows that a specific region in the C terminus of each isotype is essential for its unique function.
- ASYMMETRIC LEAVES2-LIKE19/LATERAL ORGAN BOUNDARIES DOMAIN30 and ASL20/LBD18 Regulate Tracheary Element Differentiation in Arabidopsis
Expression of ASL19 and ASL20 in immature xylem vessels depends on VND6 and VND7, two key positive regulators of xylem differentiation. ASL19/20 overexpression generates xylem-like cells and induces ectopic VND7 expression in nonvascular tissues. Thus, ASL19 and ASL20 seem to be involved in a positive feedback loop for VND6/7 expression that regulates xylem differentiation.
- Arabidopsis Synaptotagmin 1 Is Required for the Maintenance of Plasma Membrane Integrity and Cell Viability
The authors characterize an Arabidopsis syt1 mutant that exhibits reduced plasma membrane integrity. They show that SYT1 is a Ca2+-dependent phospholipid binding protein localized at the plasma membrane, and provide evidence that plasma membrane repair mediated by SYT1 is essential for cell viability in plants under nonoptimal growing conditions.
- Calcium-Dependent Freezing Tolerance in Arabidopsis Involves Membrane Resealing via Synaptotagmin SYT1
Plants surviving under subzero temperatures in winter enhance their freezing tolerance during the fall season to avoid irreversible damage to the plasma membrane. This work provides evidence that the plant synaptotagmin SYT1 functions to enhance freezing tolerance by facilitating the membrane resealing that is essential for cells to survive after the plasma membrane is damaged.
- Arabidopsis Tic40 Expression in Tobacco Chloroplasts Results in Massive Proliferation of the Inner Envelope Membrane and Upregulation of Associated Proteins
Overexpression of Tic40 in chloroplasts results in proper targeting, processing, insertion, and upregulation of other inner membrane proteins, and in massive proliferation of the inner envelope. This study opens the door for understanding membrane biogenesis, retrograde signal transduction, and use of transgenic chloroplasts for expression of membrane proteins for various biotechnology applications.
- Multiple Mechanism–Mediated Retention of a Defective Brassinosteroid Receptor in the Endoplasmic Reticulum of Arabidopsis
BRI1 is a cell surface receptor for plant steroid hormones, brassinosteriods. This work shows that bri1-5, a mutant form of BRI1 still capable of responding to the hormone, is trapped in the endoplasmic reticulum by an overvigilant quality control system using three separate retention mechanisms, and is depleted by a proteasome-independent degradation process.
- Characterization of TCTP, the Translationally Controlled Tumor Protein, from Arabidopsis thaliana
The Arabidopsis translationally controlled tumor protein (TCTP) regulates vegetative growth, lateral root formation, and root hair development,and is also critical to pollen tube growth. These effects suggest that TCTP acts in the plant TOR signalling network, as in humans and Drosophila, but with plant-specific features such as crosstalk with auxin signaling.
- Starch Granule Biosynthesis in Arabidopsis Is Abolished by Removal of All Debranching Enzymes but Restored by the Subsequent Removal of an Endoamylase
The major component of starch granules, amylopectin, is a branched glucan, the structure of which is determined by starch synthases, branching enzymes and debranching enzymes. This study reveals that when debranching enzymes are missing, amylases not normally involved in biosynthesis act on the nascent glucans, modifying their structure and thereby preventing starch granule formation.
- Lotus japonicus CASTOR and POLLUX Are Ion Channels Essential for Perinuclear Calcium Spiking in Legume Root Endosymbiosis
CASTOR and POLLUX constitute a novel class of ion channels present throughout the angiosperm lineage. Mutant phenotypes, channel properties, and subcellular localization suggest a direct involvement in the calcium spiking mechanism during nodulation in legumes.
COMMENTARY