Table of Contents
IN BRIEF
RESEARCH ARTICLES
- Arachidonic Acid: An Evolutionarily Conserved Signaling Molecule Modulates Plant Stress Signaling Networks
Oomycete pathogens contain arachidonic acid (AA), an elicitor of defense responses and programmed cell death in plants. Arabidopsis plants engineered to produce AA, or exogenously treated with this fatty acid, displayed altered resistance to biotic challengers resulting from AA’s action on salicylate and jasmonate stress signaling networks.
- Cytokinin Regulates Compound Leaf Development in Tomato
Leaf shape diversity relies on transient morphogenetic activity in leaf margins. This study identifies cytokinin as an important regulator of the extended morphogenetic activity that characterizes the leaf margin of compound tomato leaves.
- The Arabidopsis Dynamin-Related Protein2 Family Is Essential for Gametophyte Development
Both the DRP2 family of classical dynamins and the plant-specific DRP1s are thought to be required for clathrin-mediated trafficking. This study shows that the Arabidopsis DRP2 and DRP1 families have distinct developmental roles. DRP2 function was found to be necessary for cell cycle progression in the early stages of both the male and the female gametophyte development.
- Arabidopsis SET DOMAIN GROUP2 Is Required for H3K4 Trimethylation and Is Crucial for Both Sporophyte and Gametophyte Development
This study establishes that SDG2 is a major factor for histone 3 lysine 4 trimethylation in Arabidopsis and shows that loss of SDG2 causes wide-ranging defects in both sporophyte and gametophyte development.
- Inactivation of a DNA Methylation Pathway in Maize Reproductive Organs Results in Apomixis-Like Phenotypes
This study examines the molecular differences between sexual reproduction and apomixis (i.e., asexual reproduction through seeds). Profiling of sexually reproducing maize and apomictic maize-Tripsacum hybrids revealed that four loci involved in gene silencing via DNA methylation are dowregulated in apomictic plants. Plants deficient for two of these genes mimic aspects of apomictic reproduction.
- Mitochondrial β-Cyanoalanine Synthase Is Essential for Root Hair Formation in Arabidopsis thaliana
The β-cyanoalanine synthase enzyme is responsible for detoxifying the cyanide generated during cellular metabolism, primarily in the synthesis of ethylene. This analysis of a null mutant of this enzyme indicates that cyanide can act in some developmental processes as a signaling molecule.
- A Novel Factor FLOURY ENDOSPERM2 Is Involved in Regulation of Rice Grain Size and Starch Quality
The authors clone the rice FLOURY ENDOSPERM2 (FLO2) gene; flo2 mutants have aberrant endosperm, and FLO2 overexpressors have enlarged grains. Gene expression and protein interaction studies indicate that FLO2, a novel tetratricopeptide repeat containing protein, regulates storage starch and protein gene expression in rice endosperm development and may also play a role in heat tolerance.
- The ER-Localized TWD1 Immunophilin Is Necessary for Localization of Multidrug Resistance-Like Proteins Required for Polar Auxin Transport in Arabidopsis Roots
Members of the B group of ABC transporters are required for polar auxin transport through various plant tissues and organs. This report clarifies how the TWD1 immunophilin affects auxin transport and root growth by affecting B-group ABC transporters.
- A Maize Thiamine Auxotroph Is Defective in Shoot Meristem Maintenance
Mutations in the maize thiamine biosynthesis gene bladekiller1 induce meristem abortion phenotypes that are completely rescued by exogenous thiamine. The data illustrate the essential role of metabolic cofactors during the proliferative growth of the undifferentiated stem cell populations that comprise plant meristems.
- RAD5A, RECQ4A, and MUS81 Have Specific Functions in Homologous Recombination and Define Different Pathways of DNA Repair in Arabidopsis thaliana
The processing of complex DNA intermediates in replication and repair is essential. This work defines the role of two ATPases, RAD5A and RECQ4A, and the endonuclease MUS81 in DNA repair and recombination in Arabidopsis. It shows that all three proteins are involved in different pathways of DNA repair and have specific roles in double-strand break–induced homologous recombination.
- Regulation of the Chlamydomonas Cell Cycle by a Stable, Chromatin-Associated Retinoblastoma Tumor Suppressor Complex
The retinoblastoma (RB) pathway is a conserved eukaryotic cell cycle regulator that is thought to control cell cycle progression through periodic dissociation of the repressor protein, RB, from the activator proteins E2F and DP. This study shows that in the unicellular alga Chlamydomonas, the cell cycle is regulated by a constitutively chromatin-bound RB-E2F-DP ternary complex whose subunits do not undergo periodic dissociation.
- Provitamin A Accumulation in Cassava (Manihot esculenta) Roots Driven by a Single Nucleotide Polymorphism in a Phytoene Synthase Gene
Cassava is a very important staple crop, especially in the arid tropics where it is a chief source of carbohydrates, but the provitamin A content in the storage root is insufficient to sustain a healthy life. The work presented shows that a single amino acid exchange in a conserved region of the enzyme phytoene synthase leads to substantive accumulation of β-carotene (provitamin A) in the roots.
- Functional Analyses of Caffeic Acid O-Methyltransferase and Cinnamoyl-CoA-Reductase Genes from Perennial Ryegrass (Lolium perenne)
The authors show enhanced digestibility of cinnamoyl CoA-reductase and caffeic acid O-methyltransferase-deficient perennial ryegrass plants grown under glasshouse and field conditions. This indicates that both of these lignin biosynthetic genes are promising targets for transgenic approaches aiming to enhance forage quality and improve feedstock plants for biofuel production.
- A Novel Glucosylation Reaction on Anthocyanins Catalyzed by Acyl-Glucose–Dependent Glucosyltransferase in the Petals of Carnation and Delphinium
This work describes a glucosylation reaction at the 5/7 positions of anthocyanins in the petals of carnations and delphiniums. Unusually, this reaction is catalyzed by acyl-glucose–dependent glucosyltransferases that belong to glycoside hydrolase family 1. This modification mechanism may play an important role in generating variation in anthocyanins.
- Clustered Transcription Factor Genes Regulate Nicotine Biosynthesis in Tobacco
This work examines the molecular lesions responsible for the low-nicotine phenotype of a classical tobacco mutant. Extensive duplications of genes encoding jasmonate-responsive transcription factors, found at the NIC2 locus, offer new insights into how regulatory genes for alkaloid biosynthesis are organized and evolved.
- Nonflowering Plants Possess a Unique Folate-Dependent Phenylalanine Hydroxylase That Is Localized in Chloroplasts
This work identified aromatic amino acid hydroxylase (AAH)-like sequences from nonflowering plants. The encoded proteins were shown to be plastid targeted, to have Phe hydroxylase activity, and, unlike animal and bacterial AAHs, to use a folate as cofactor rather than a pterin. Ablating AAH in moss led to accumulation of Phe and caffeate esters.
- The Cytoskeleton and the Peroxisomal-Targeted SNOWY COTYLEDON3 Protein Are Required for Chloroplast Development in Arabidopsis
This report characterizes snowy cotyledon3, a mutant with disrupted chloroplast development that reveals a requirement for the cytoskeleton and peroxisomes in chloroplast biogenesis.
- The Arabidopsis Thylakoid Protein PAM68 Is Required for Efficient D1 Biogenesis and Photosystem II Assembly
This work shows that PAM68 is a previously unknown PSII assembly factor that is required for efficient accumulation of photosystem II complexes in Arabidopsis thaliana and that is involved in early steps of PSII assembly in Synechocystis and Arabidopsis.
- Arabidopsis VASCULAR-RELATED NAC-DOMAIN6 Directly Regulates the Genes That Govern Programmed Cell Death and Secondary Wall Formation during Xylem Differentiation
This article reports the identification of the downstream genes regulated by a master regulator of differentiation of tracheary elements, VND6, and of xylem fibers, SND1. VND6 was found to directly regulate several genes involved in programmed cell death and secondary cell wall formation through binding to a specific cis-element.
- The Medicago truncatula E3 Ubiquitin Ligase PUB1 Interacts with the LYK3 Symbiotic Receptor and Negatively Regulates Infection and Nodulation
Partner specificity in legume-rhizobia symbiosis involves perception of rhizobial signals by plant lysin motif receptor-like kinases (LysM-RLKs) leading to the formation of nitrogen-fixing root nodules. This work describes PUB1, a protein interactor of LYK3 LysM-RLK, which is involved in regulating the specificity of interaction between Medicago truncatula and Sinorhizobium meliloti.
- Norcoclaurine Synthase Is a Member of the Pathogenesis-Related 10/Bet v1 Protein Family
Norcoclaurine synthase (NCS) catalyzes the first step in the formation of benzylisoquinoline alkaloids, which include the painkillers morphine and codeine. Two different enzymes identified as norcoclaurine synthase have been reported. Characterization of NCS in opium poppy and meadow rue has shown that only the enzyme belonging to the PR10/Bet v1 protein family is involved in norcoclaurine biosynthesis.
