Table of Contents
IN BRIEF
LETTER TO THE EDITOR
RESEARCH ARTICLES
- Origins and Recombination of the Bacterial-Sized Multichromosomal Mitochondrial Genome of Cucumber
This work presents the cucumber mitochondrial genome sequence. Its extremely large size reflects the proliferation of dispersed repeats, large introns, and an abundance of chloroplast and nuclear DNA. The genome has an unusual multichromosomal structure, and computational analyses reveal a large number of recombinationally active repeats.
- Genome-Wide Binding Site Analysis of FAR-RED ELONGATED HYPOCOTYL3 Reveals Its Novel Function in Arabidopsis Development
This work analyzed genome-wide binding sites of a transposase-derived transcription factor, FHY3, using a chromatin immunoprecipitation–based sequencing approach and identified a role for FHY3 in controlling chloroplast development by directly activating the expression of ARC5, a key gene involved in chloroplast division.
- Rice MADS6 Interacts with the Floral Homeotic Genes SUPERWOMAN1, MADS3, MADS58, MADS13, and DROOPING LEAF in Specifying Floral Organ Identities and Meristem Fate
This work shows that the rice AGAMOUS-LIKE6 MADS box gene MADS6 acts as a master regulator in specifying floral organ identities and meristem determinacy through interaction with B-, C-, D-, and E-class floral homeotic genes.
- Arabidopsis Class I KNOTTED-Like Homeobox Proteins Act Downstream in the IDA-HAE/HSL2 Floral Abscission Signaling Pathway
This work reports the characterization of a new mutant allele of the KNOX gene BP/KNAT1 and reveals that BP/KNAT1 inhibits floral organ abscission in Arabidopsis by restricting abscission zone cell size and number. It puts forward a model whereby IDA signaling suppresses BP/KNAT1, which in turn allows KNAT2 and KNAT6 to induce floral organ abscission.
- Induction of Dormancy in Arabidopsis Summer Annuals Requires Parallel Regulation of DOG1 and Hormone Metabolism by Low Temperature and CBF Transcription Factors
In plants grown under field conditions, seed dormancy varies considerably with the time of year the seed is set, and this variation is important for the coordination of plant life history and seed quality. This work elucidates the mechanisms through which environmental temperature during seed set affects the germination behavior of seeds when released from the mother plant.
- Distinct Cell-Autonomous Functions of RETINOBLASTOMA-RELATED in Arabidopsis Stem Cells Revealed by the Brother of Brainbow Clonal Analysis System
We constructed a CRE/lox clonal deletion system named BOB (Brother of Brainbow), which allows tissue-specific elimination of gametophytic essential genes from desired cells. The null sectors, marked by a combination of fluorescent proteins, show that genomic removal of RBR leads to cell-autonomous overproliferation of the quiescent center and distal columella stem cells.
- Differential Regulation of Cellulose Orientation at the Inner and Outer Face of Epidermal Cells in the Arabidopsis Hypocotyl
Whereas microtubules and cellulose synthase trajectories are transversely oriented on the outer epidermal surface of Arabidopsis hypocotyl cells only for part of the growth cycle, microtubules and microfibrils at the inner surface remain transverse throughout growth. The inner face of the epidermis is thus established as a regulator of growth anisotropy in the hypocotyl.
- Augmin Plays a Critical Role in Organizing the Spindle and Phragmoplast Microtubule Arrays in Arabidopsis
Two augmin complex proteins, which play a critical role in microtubule organization in the spindle and phragmoplast during cell division of plant cells, are identified in this study.
- Control of Hydrogen Photoproduction by the Proton Gradient Generated by Cyclic Electron Flow in Chlamydomonas reinhardtii
This work describes a Chlamydomonas mutant (pgrl1) isolated from a screen designed to identify new photosynthetic regulatory mechanisms. It provides evidence that in the wild type, photosynthetic electron supply to hydrogenase is severely limited by the proton gradient generated by cyclic electron flow, opening new perspective towards optimizing hydrogen production by microalgae.
- In Vitro Reconstitution of the Cyanobacterial Photoprotective Mechanism Mediated by the Orange Carotenoid Protein in Synechocystis PCC 6803
In the cyanobacterial photoprotective mechanism, one red-activated Orange Carotenoid Protein binds to the core of the phycobilisome and quenches all its fluorescence. This binding stabilizes the red form. Addition of the Fluorescence Recovery Protein accelerates fluorescence recovery in darkness by interacting with the red protein and destabilizing its binding to the phycobilisome.
- A Monogalactosyldiacylglycerol Synthase Found in the Green Sulfur Bacterium Chlorobaculum tepidum Reveals Important Roles for Galactolipids in Photosynthesis
The authors identified a bacterial monogalactosyldiacylglycerol synthase enzyme from Chlorobaculum tepidum. Using complementation analysis of a galactolipid synthase mutant of Arabidopsis, they revealed crucial roles of galactolipids for plant and bacterial photosynthesis. In addition, they investigated and discuss evolutionary paths of galactolipid biosynthesis in phototrophs.
- Arabidopsis Mutants Deleted in the Light-Harvesting Protein Lhcb4 Have a Disrupted Photosystem II Macrostructure and Are Defective in Photoprotection
Analysis of a series of mutants lacking each of the three isoforms of the Lhcb4 light-harvesting complex in Arabidopsis showed that this complex plays an important role in the macro-organization and photoprotection of photosystem II.
- Recruitment of a Ribosomal Release Factor for Light- and Stress-Dependent Regulation of petB Transcript Stability in Arabidopsis Chloroplasts
The plastid ribosomal release factor-like protein PrfB3 arose from a gene duplication and has subsequently lost the two most important tripeptide motifs required for stop codon recognition and catalysis. This work shows that PrfB3 is essential in vascular plants and has been recruited for binding and environment-dependent stabilization of petB RNA to regulate cytochrome b6f complex levels.
- A Novel Calcium Binding Site in the Slow Vacuolar Cation Channel TPC1 Senses Luminal Calcium Levels
The slow vacuolar channel is the dominant cation channel of the vacuolar membrane and is regulated by cytosolic as well as vacuolar calcium. Here, the vacuolar calcium binding site is characterized at the molecular level, adding to our understanding of calcium signaling in the extracytosolic space.
- Independent Recruitment of an O-Methyltransferase for Syringyl Lignin Biosynthesis in Selaginella moellendorffii
This study examines the lignin biosynthesis pathway in the lycophyte Selaginella moellendorffii. An O-methyltransferase gene was found clustered with the gene encoding a phenylpropanoid meta-hydroxylase known to catalyze the formation of syringyl lignin subunits. The O-methyltransferase is shown to function in the same enzymatic pathway as the phenylpropanoid meta-hydroxylase.
- The FRD3 Citrate Effluxer Promotes Iron Nutrition between Symplastically Disconnected Tissues throughout Arabidopsis Development
This work examines the role of the citrate transporter FRD3 in iron homeostasis during plant development, finding key roles in pollen and embryo development, and in leaf, in addition to its known role in roots and in the apoplastic transport of iron.
- Identification of Genes in the Phenylalanine Metabolic Pathway by Ectopic Expression of a MYB Transcription Factor in Tomato Fruit
Ectopic expression of a MYB transcription factor, ODO1, in tomato fruit altered Phe and phenylpropanoid metabolism, as shown by metabolic profiling and flux analysis. This disruption permitted identification of a set of coregulated genes, including prephenate aminotransferase, which converts prephenate to arogenate. The results establish a fruit arogenate pathway for Phe synthesis.
- The Defective Proteasome but Not Substrate Recognition Function Is Responsible for the Null Phenotypes of the Arabidopsis Proteasome Subunit RPN10
This study shows that the major ubiquitin receptors involved in targeting ubiquitylated proteins for proteasome-mediated proteolysis are functionally redundant in Arabidopsis. Interestingly, in addition to playing a redundant role in substrate recognition, the Arabidopsis proteasome subunit RPN10 maintains the structural integrity of proteasome, which is critical for vegetative and reproductive growth.
- Symbiotic Rhizobia Bacteria Trigger a Change in Localization and Dynamics of the Medicago truncatula Receptor Kinase LYK3
This work localizes a functional LYK3-GFP protein in roots prior to and during establishment of rhizobial symbiosis. Experiments show that LYK3-GFP dynamics and localization are affected by symbiotic bacteria in a Nod Factor signal-dependent manner and that postinoculation LYK3-GFP codistributes with a tagged plant flotillin.
- Perturbation of Arabidopsis Amino Acid Metabolism Causes Incompatibility with the Adapted Biotrophic Pathogen Hyaloperonospora arabidopsidis
This work identified two different Arabidopsis mutants that have reduced susceptibility to an infectious biotrophic pathogen due to overaccumulation of the amino acid Thr. This is detrimental for the host plant and the infecting pathogen but does not affect disease caused by some other pathogen species. Therefore, the host metabolic state can influence disease in quite a specific manner.
