Table of Contents
IN BRIEF
REVIEW ARTICLES
RESEARCH ARTICLES
- Global Identification of Targets of the Arabidopsis MADS Domain Protein AGAMOUS-Like15
This study examines the numbers and types of genes directly and indirectly regulated by the MADS domain protein AGL15 in embryo tissue. Further work verified association of AGL15 with regulatory regions of genes encoding key regulators of embryo development and documented the response of these genes to AGL15 accumulation.
- bearded-ear Encodes a MADS Box Transcription Factor Critical for Maize Floral Development
bearded-ear encodes an AGL6-like MADS box transcription factor that is required for floral meristem determinacy, floral organ development, and sex determination in maize.
- Evolution of AGL6-like MADS Box Genes in Grasses (Poaceae): Ovule Expression Is Ancient and Palea Expression Is New
This work examines the evolutionary relationships and developmental expression patterns of MADS box genes related to AGAMOUS-like6 (AGL6). Using multiple grass species, the authors find that AGL6-like family members have acquired gene expression domains during the evolution of grasses, indicating diverse roles in floral development.
- Evolutionarily Conserved Regulatory Motifs in the Promoter of the Arabidopsis Clock Gene LATE ELONGATED HYPOCOTYL
This work combines traditional analysis of deletion constructs, biochemistry, and bioinformatics to identify regulatory elements within the LATE ELONGATED HYPOCOTY promoter. A G-box motif and a novel element related to CArG boxes are shown to contribute to circadian-regulated transcription.
- Cryptochromes, Phytochromes, and COP1 Regulate Light-Controlled Stomatal Development in Arabidopsis
Cryptochromes (CRY), phytochromes (phy), and COP1 regulate a variety of light-controlled developmental processes. The authors show in this report that CRY, phyA, and phyB act together to promote stomatal development, whereas COP1 acts constitutively to repress stomatal development. CRY, phyA, phyB, and COP1 act genetically in parallel with TMM but upstream of YDA, SPCH, MUTE, and FAMA, respectively.
- A Dual Role for the S-Locus Receptor Kinase in Self-Incompatibility and Pistil Development Revealed by an Arabidopsis rdr6 Mutation
A mutation in the RNA-dependent RNA polymerase RDR6 simultaneously enhances self-incompatibility and causes stigma exsertion, the extent of which is magnified in the presence of a catalytically active S-locus receptor kinase. The data implicate trans-acting small-inhibitory RNA in the regulation of both processes and provides a molecular explanation for their coordinate evolution.
- Cellular Pathways Regulating Responses to Compatible and Self-Incompatible Pollen in Brassica and Arabidopsis Stigmas Intersect at Exo70A1, a Putative Component of the Exocyst Complex
This work identifies Exo70A1 as a compatibility factor required in Brassica and Arabidopsis stigmatic papillae for accepting compatible pollen. Exo70A1 acts early in this process to regulate both pollen hydration and pollen tube penetration into the stigmatic surface. Furthermore, Exo70A1 is negatively regulated by the Brassica self-incompatibility response to rapidly reject self pollen.
- The MYB305 Transcription Factor Regulates Expression of Nectarin Genes in the Ornamental Tobacco Floral Nectary
Ornamental tobacco nectar contains five proteins that function via the nectar redox cycle to protect the gynoecium from pollinator-borne microorganisms. Two of these proteins, Nectarin I and Nectarin V, are regulated by the MYB305 transcription factor, which also regulates flavonoid biosynthetic genes.
- The STRUCTURAL MAINTENANCE OF CHROMOSOMES 5/6 Complex Promotes Sister Chromatid Alignment and Homologous Recombination after DNA Damage in Arabidopsis thaliana
Physical proximity between donor and acceptor DNA strands is essential for homologous recombination. Here, it is shown that SYN1-dependent S phase cohesion, SMC6A, SMC6B, and likely also SMC5 are required for DNA damage-dependent enhancement of sister chromatid alignment. SMC6A and SMC6B are additionally needed for somatic homologous recombination between sister chromatids in Arabidopsis.
- Replication Stress Leads to Genome Instabilities in Arabidopsis DNA Polymerase δ Mutants
Replication of the genetic information is the basis of life. Arabidopsis plants with reduced levels of the DNA synthesizing enzyme, Polymerase δ, suffer from severe defects in this process, which leads to dangerous DNA breaks. Sophisticated pathways ensure that these lesions are repaired by an error-free homology-based mechanism that can be visualized as spots on the plants.
- Dynamic Plastid Redox Signals Integrate Gene Expression and Metabolism to Induce Distinct Metabolic States in Photosynthetic Acclimation in Arabidopsis
Fluctuating light affects plant photosynthetic electron transport, resulting in redox changes of transport chain components. These changes act as active signals that control expression of genes for photosynthesis and metabolism in two distinct and differential adjustment loops, resulting in appropriate acclimation responses that adapt plant primary production and growth to the residing environment.
- The ABC Transporter PXA1 and Peroxisomal β-Oxidation Are Vital for Metabolism in Mature Leaves of Arabidopsis during Extended Darkness
This work examines the role of fatty acid β-oxidation in mature leaves exposed to extended darkness. Mutants defective in peroxisomal lipid metabolism accumulate toxic amounts of free fatty acids and chlorophyll breakdown products in conditions such as extended darkness where carbohydrate energy reserves are depleted.
- The Arabidopsis Nitrate Transporter NRT1.7, Expressed in Phloem, Is Responsible for Source-to-Sink Remobilization of Nitrate
This study of nitrate transporter NRT1.7 showed that nitrate itself can be remobilized from older leaves to younger leaves, and nitrate remobilization is mediated by phloem. Growth retardation of nrt1.7 mutants under N starvation conditions indicated that nitrate remobilization is key for nitrogen use efficiency.
- Phage-Type RNA Polymerase RPOTmp Performs Gene-Specific Transcription in Mitochondria of Arabidopsis thaliana
The RNA polymerase RPOTmp transcribes a subset of mitochondrial genes. The gene selectivity of this enzyme is not mediated by promoter sequence specificity. Transcripts made by RPOTmp are required for the biogenesis of respiratory chain complexes I and IV, revealing that transcription affects protein abundance in mitochondria.
- Genome-Wide Medicago truncatula Small RNA Analysis Revealed Novel MicroRNAs and Isoforms Differentially Regulated in Roots and Nodules
Large-scale pyrosequencing of small RNAs from Medicago truncatula root tips and indeterminate nitrogen-fixing nodules identified 36 miRNA families already registered in plants and 100 novel miRNA candidates encoded by 265 precursors. The organ- and tissue-specific accumulation of certain miRNAs suggests diverse roles in nodule meristems, cell differentiation, and interaction with symbiotic bacteria.
- A Small GTPase of the Rab Family Is Required for Root Hair Formation and Preinfection Stages of the Common Bean–Rhizobium Symbiotic Association
This work characterizes a small GTPase that participates in the genesis and growth of root hairs. This protein is required for the reorientation of root hair polar growth that follows rhizobia perception, providing a link between vesicle traffic and the infection process that leads to nodulation.
- Medicago N2-Fixing Symbiosomes Acquire the Endocytic Identity Marker Rab7 but Delay the Acquisition of Vacuolar Identity
This work examines molecular identity markers of the host endomembrane system during the formation of nitrogen-fixing symbiosome organelles in Medicago. In addition to plasma membrane markers, symbiosomes initially show markers of late endosomes but do not develop into lytic vacuoles; this suspended developmental state allows the organelles to harbor the symbiotic Rhizobium bacteria.
- The Heat Shock Response in Moss Plants Is Regulated by Specific Calcium-Permeable Channels in the Plasma Membrane
Activation of heat shock genes is a highly conserved response to elevated temperature. Here, biomonitoring, electrophysiological, and pharmacological approaches show that during a temperature rise, the plasma membrane of moss cells is the earliest regulator of a specific calcium-dependent signaling pathway leading to the expression of heat shock proteins and the establishment of thermotolerance.
- The Rice α-Amylase Glycoprotein Is Targeted from the Golgi Apparatus through the Secretory Pathway to the Plastids
Protein targeting into plastids is an essential cellular event for maintaining plant function and life. This work contributes to the understanding of a novel pathway for targeting of α-amylase glycoproteins from the endomembrane system into the plastids, which involves direct communication between the Golgi apparatus and the plastids.
- A Tripartite SNARE-K+ Channel Complex Mediates in Channel-Dependent K+ Nutrition in Arabidopsis
A vesicle trafficking protein that contributes to secretion at the plasma membrane of Arabidopsis also binds directly to a regulatory K+ channel subunit and modifies channel activity to facilitate K+ nutrient acquisition
- A Transporter at the Node Responsible for Intervascular Transfer of Silicon in Rice
Minerals taken up by the roots are normally redirected at plant nodes before finally being transported into developing seeds. This work describes a transporter that is involved in the intervascular transfer of silicon from large vascular bundles coming from the roots to diffuse vascular bundles connected to the panicles.
- MAP KINASE PHOSPHATASE1 and PROTEIN TYROSINE PHOSPHATASE1 Are Repressors of Salicylic Acid Synthesis and SNC1-Mediated Responses in Arabidopsis
This work identifies the function of two protein phosphatases, MKP1 and PTP1, as repressors of biotic stress responses in Arabidopsis. This function is essential for normal growth and development, increasing our understanding on the importance of negative regulators of MAP kinases and the suppression of aberrant biotic stress signaling in vivo.
- Specific Targeting of the Arabidopsis Resistance Protein RPW8.2 to the Interfacial Membrane Encasing the Fungal Haustorium Renders Broad-Spectrum Resistance to Powdery Mildew
Many fungal and oomycete pathogens rely on a feeding structure, the haustorium, to extract nutrition from the plant cell. In response, the Arabidopsis resistance protein RPW8.2 is targeted to the extrahaustorial membrane to constrain the haustorium, rendering broad-spectrum resistance.
- Autophagy Negatively Regulates Cell Death by Controlling NPR1-Dependent Salicylic Acid Signaling during Senescence and the Innate Immune Response in Arabidopsis
Autophagy-defective mutants (atg mutants) exhibit an early cell death phenotype during senescence and during the innate immune response. Biochemical, pharmacological, and genetic analyses reveal that excessive salicylic acid (SA) signaling is a major factor in atg-dependent cell death, suggesting a physiological function of autophagy that operates a negative feedback loop modulating SA signaling.
- In Planta Expression Screens of Phytophthora infestans RXLR Effectors Reveal Diverse Phenotypes, Including Activation of the Solanum bulbocastanum Disease Resistance Protein Rpi-blb2
This study describes activity screens of a collection of RXLR-type effectors from the Irish potato famine pathogen based on expression inside plant cells. The diverse activities ascribed here to several RXLR effectors support the view that these proteins form a critical class of host translocated effectors in oomycetes, some of which are targeted by the plant immune system.
- Agrobacterium tumefaciens Promotes Tumor Induction by Modulating Pathogen Defense in Arabidopsis thaliana
Transcriptome and metabolite analysis of three stages of Agrobacterium–Arabidopsis interaction revealed that auxin, ethylene, and salicylic acid are the main players during the course of crown gall development. Their sequential and concerted action seems to stabilize a balance between pathogen defense launched by the host and tumor growth initiated by agrobacteria.
- Actin-Depolymerizing Factor2-Mediated Actin Dynamics Are Essential for Root-Knot Nematode Infection of Arabidopsis
The actin-depolymerizing factor ADF2 is upregulated at the site of infection of endoparasitic root-knot nematodes. Reducing the level of ADF2 causes the stabilization of F-actin in the feeding cells and arrests their development, resulting in an unsuccessful infection. Our data show that ADF-mediated modeling of the actin cytoskeleton is essential for a susceptible nematode-plant interaction.
