Table of Contents
IN BRIEF
RESEARCH ARTICLES
- Redefining C and D in the Petunia ABC
The petunia AGAMOUS subfamily of MADS box transcription factors contains two C- and two D-lineage genes. This work shows that the two C-genes redundantly specify stamen and carpel identity, whereas all four genes participate in ovule identity specification and floral meristem termination. These results illustrate that subfunctionalization among homeotic genes can vary considerably between species.
- Leaf Asymmetry as a Developmental Constraint Imposed by Auxin-Dependent Phyllotactic Patterning
Superficially, many angiosperm leaves appear bilaterally symmetric. However, is there a systematic source of asymmetry in leaves? This work describes left-right asymmetries in tomato and Arabidopsis thaliana leaves that are dependent on phyllotactic direction. Using modeling and empirical results, the authors infer such asymmetry arises via biased auxin distribution in leaf primordia.
- Antisense Inhibition of the 2-Oxoglutarate Dehydrogenase Complex in Tomato Demonstrates Its Importance for Plant Respiration and during Leaf Senescence and Fruit Maturation
Here, antisense inhibition of the E1 subunit of the 2-oxoglutarate dehydrogenase complex in tomato was associated with generally accelerated development. This report reveals the importance of this mitochondrial enzyme in both photosynthetic and respiratory metabolism, highlighting its significance in programs of plant development connected to carbon–nitrogen interactions.
- A shrunken-2 Transgene Increases Maize Yield by Acting in Maternal Tissues to Increase the Frequency of Seed Development
This work examines the function of a maize heat-stable, less inhibitor–sensitive form of ADP-glucose pyrophosphorylase, which increases maize yield by increasing seed number. This work shows that this increase requires high temperature during early seed development and results from transgene function in maternal tissues to increase the probability that an ovary will produce a seed.
- Epistatic Natural Allelic Variation Reveals a Function of AGAMOUS-LIKE6 in Axillary Bud Formation in Arabidopsis
This study identified a natural allele of AGAMOUS-Like6 that correlated with reduced stem branching in late-flowering accessions of Arabidopsis.
- Nicotianamine Functions in the Phloem-Based Transport of Iron to Sink Organs, in Pollen Development and Pollen Tube Growth in Arabidopsis
This work analyzes the effect of the metal chelator nicotianamine on plant growth and development. It reveals that the transport of Fe from phloem to sink organs depends on nicotianamine and that this chelator has a role in pollen germination and transfer through the style.
- Gsp1 Triggers the Sexual Developmental Program Including Inheritance of Chloroplast DNA and Mitochondrial DNA in Chlamydomonas reinhardtii
This study examined a mutant of Chlamydomonas reinhardtii, biparental31, defective in the sexual development upon the fusion of male (mating type minus [mt−]) and female (mt+) gametes and demonstrated the importance of a homeoprotein gene (GSP1) and inositol metabolism in orchestrating the sexual program, including uniparental inheritance of chloroplast and mitochondrial DNA.
- Preferential Retention of Circadian Clock Genes during Diploidization following Whole Genome Triplication in Brassica rapa
Whole genome duplication is typically followed by considerable gene loss, during which the gene dosage hypothesis predicts the preferential retention of highly networked or dose-sensitive genes. Here, circadian clock genes are found to conform to the gene dosage hypothesis in Brassica rapa, consistent with the current model of the circadian clock as a key regulator of multiple cellular pathways.
- A Self-Regulatory Circuit of CIRCADIAN CLOCK-ASSOCIATED1 Underlies the Circadian Clock Regulation of Temperature Responses in Arabidopsis
The CCA1 MYB transcription factor is a component of the circadian clock, which plays an important role in plant responses to cold temperatures. This work shows that cold temperatures regulate CCA1 activity by modulating CCA1 alternative splicing and thus altering the molecular ratios of alternatively spliced isoforms to induce cold tolerance responses.
- Metabolism and Growth in Arabidopsis Depend on the Daytime Temperature but Are Temperature-Compensated against Cool Nights
This study investigated the response of metabolism and growth to fluctuating temperatures under carbon-limiting conditions (short days, low light). It is shown that biomass production is determined largely by the daytime temperature via its effect on photosynthesis. By contrast, the mobilization of starch and use of carbon for growth is compensated against changes in the night temperature.
- Arabidopsis PYR/PYL/RCAR Receptors Play a Major Role in Quantitative Regulation of Stomatal Aperture and Transcriptional Response to Abscisic Acid
A mutant lacking six abscisic acid (ABA) receptors and ABA-mediated activation of SnRK2.2/2.3/2.6 kinases shows an extreme ABA-insensitive phenotype, even though other branches for ABA perception remain functional. ABA perception through PYR/PYL/RCAR receptors plays a major role in regulating seed germination and establishment, vegetative and reproductive growth, stomatal aperture, and transcriptional response to ABA.
- A PP6-Type Phosphatase Holoenzyme Directly Regulates PIN Phosphorylation and Auxin Efflux in Arabidopsis
This work shows that three proteins (i.e., FyPP1/3, SAL, and PP2AA) interact to form a protein phosphatase 6 heterotrimeric holoenzyme complex that regulates PIN phosphorylation and polar localization and thereby determines auxin transport polarity.
- Auxin Controls Arabidopsis Adventitious Root Initiation by Regulating Jasmonic Acid Homeostasis
Vegetative propagation of plants from shoots requires the development of adventitious roots that regenerate from stem cuttings. Multiple endogenous and environmental factors control this complex process; this study in the model plant Arabidopsis thaliana shows that adventitious rooting is an adaptive developmental response involving crosstalk between auxin and jasmonate signaling pathways.
- The Recent Evolution of a Symbiotic Ion Channel in the Legume Family Altered Ion Conductance and Improved Functionality in Calcium Signaling
Two similar but not redundant ion channels (CASTOR and POLLUX) are required for the transduction of symbiotic signals in angiosperms. A single amino acid substitution in the filter region of POLLUX occurred recently in the legume family. This mutation altered POLLUX conductance and improved its functionality, while relegating CASTOR to a minor role in the corresponding legume tribes.
- A Plasma Membrane Receptor Kinase, GHR1, Mediates Abscisic Acid- and Hydrogen Peroxide-Regulated Stomatal Movement in Arabidopsis
An Arabidopsis gene, GUARD CELL HYDROGEN PEROXIDE RESISTANT1 (GHR1), was identified and found to encode a receptor-like kinase localized on the plasma membrane. GHR1 directly phosphorylates and activates the S-type anion channel SLAC1 in Xenopus oocytes, which is negatively regulated by ABI2.
- DWARF AND LOW-TILLERING Acts as a Direct Downstream Target of a GSK3/SHAGGY-Like Kinase to Mediate Brassinosteroid Responses in Rice
DLT plays a positive role in brassinosteroid (BR) signaling, but the mechanism of its action is not fully understood. This study identifies a GSK3-like kinase (GSK2) as a critical negative regulator of BR signaling in rice and provides evidence that GSK2 phosphorylates and regulates DLT to regulate BR responses.
- Ethylene Signaling Negatively Regulates Freezing Tolerance by Repressing Expression of CBF and Type-A ARR Genes in Arabidopsis
This work examines the function of ethylene in freezing in Arabidopsis thaliana, finding that ethylene negatively regulates freezing stress signaling through the direct repression of cold-regulated CBF and type-A Arabidopsis response regulator genes targeted by EIN3.
- Identification of a Photosystem II Phosphatase Involved in Light Acclimation in Arabidopsis
Thylakoid protein phosphorylation plays a central role in the dynamic acclimation of the photosynthetic electron transfer chain to changing light conditions. This work identifies a protein phosphatase that is required for dephosphorylation of photosystem II subunits and counteracts the activity of the protein kinase STN8.
- Degradation of Arabidopsis CRY2 Is Regulated by SPA Proteins and Phytochrome A
This work examines the role of SUPPRESSOR OF PHYA-105 (SPA) protein family members in degradation of the UV-A/blue light photoreceptor cryptochrome 2 (cry2) and shows that SPAs and phytochrome A promote this process under low fluence rates of blue light most likely by a direct interaction of SPAs with cry2.
- Demethylesterification of the Primary Wall by PECTIN METHYLESTERASE35 Provides Mechanical Support to the Arabidopsis Stem
The ability of secondary cell walls to provide mechanical support to plant stems is well known. This work shows that primary cell walls also provide support. PECTIN METHYLESTERASE35 strengthens Arabidopsis thaliana shoots by demethylesterifying homogalacturonan in primary cell walls, including the middle lamella.
- Arabidopsis MYC2 Interacts with DELLA Proteins in Regulating Sesquiterpene Synthase Gene Expression
This work examines the regulation of two sesquiterpene synthases and shows that gibberellin and jasmonate jointly regulate the biosynthesis of sesquiterpenes through the transcription factor MYC2, and the gibberellin signal is transduced to this secondary metabolism pathway through a DELLA–MYC2 interaction
- Fe Sparing and Fe Recycling Contribute to Increased Superoxide Dismutase Capacity in Iron-Starved Chlamydomonas reinhardtii
Two pathways increase the capacity of the Chlamydomonas chloroplast to detoxify superoxide during Fe limitation stress. In one, a novel plastid-localized MnSOD is expressed in response to Fe limitation. In a second pathway, the plastid FeSOD is preferentially retained over other abundant Fe proteins, demonstrating prioritized allocation of Fe within the chloroplast.
- Crystal Structure of Arabidopsis Cyclophilin38 Reveals a Previously Uncharacterized Immunophilin Fold and a Possible Autoinhibitory Mechanism
The crystal structure of CYP38, a proposed photosystem II assembly factor, is reported at 2.39-Å resolution. The structure, along with functional assays, suggests that CYP38 is not an active peptidyl-prolyl cis/trans isomerase, and interaction of the N-terminal helical domain with the putative C-terminal cyclophilin domain implies that CYP38 functions as a chaperone via an intramolecular autoinhibition mechanism.
- Dual Location of the Mitochondrial Preprotein Transporters B14.7 and Tim23-2 in Complex I and the TIM17:23 Complex in Arabidopsis Links Mitochondrial Activity and Biogenesis
This work shows that the preprotein transporters B14.7 and Tim23.2 accumulate in two mitochondrial protein complexes: the respiratory chain complex I and the protein import complex TIM17:23, and that the abundance of complex I is inversely related to the abundance of Tim23. This could serve to activate mitochondrial biogenesis under conditions that damage complex I (e.g. oxidative damage or increased respiratory demand).
- Structure of Soybean β-Cyanoalanine Synthase and the Molecular Basis for Cyanide Detoxification in Plants
β-Cyanoalanine synthase detoxifies cyanide, which is produced during ethylene biosynthesis. The three-dimensional structure of β-cyanoalanine synthase provides a molecular view of how this enzyme performs its protective function and reveals evolutionary changes in the active site that distinguish it from other related enzymes.
COMMENTARY