Table of Contents
IN BRIEF
LARGE-SCALE BIOLOGY ARTICLES
Comprehensive Protein-Based Artificial MicroRNA Screens for Effective Gene Silencing in PlantsThis work uses a facile protein-based screen to systematically examine the efficacy and action mechanism of amiRNAs, thereby allowing selection of optimal amiRNAs for gene silencing from hundreds of computationally predicted candidates.
Advanced Proteomic Analyses Yield a Deep Catalog of Ubiquitylation Targets in ArabidopsisThe posttranslation addition of ubiquitin plays a central role in defining the functions, interactions, trafficking, and/or turnover of many intracellular proteins. This study employed advanced proteomics to generate a comprehensive catalog of ubiquitylation substrates from Arabidopsis, providing a detailed view into the diverse array of regulatory and metabolic processes under its control.
RESEARCH ARTICLES
Deciphering the Diploid Ancestral Genome of the Mesohexaploid Brassica rapaThis work reports on the reconstruction of the three diploid Brassica genomes with seven chromosomes involved in the origin of the hexaploid Brassica ancestor with 42 chromosomes. The hexaploid genome evolved through extensive genome diploidization toward extant diploid-like Brassica genomes.
MicroRNA Superfamilies Descended from miR390 and Their Roles in Secondary Small Interfering RNA Biogenesis in EudicotsThis work shows the conservation in eudicots of a miRNA-TAS-PPR-siRNA pathway characterized by a set of 22-nucleotide miRNAs that trigger secondary siRNAs using distinct mechanistic strategies. This super-miR7122 family of miRNAs includes miR173 and originates from miR390, emerging via gene duplication and neofunctionalization, which involved yet another miRNA superfamily (super-miR4376).
oiwa, a Female Gametophytic Mutant Impaired in a Mitochondrial Manganese-Superoxide Dismutase, Reveals Crucial Roles for Reactive Oxygen Species during Embryo Sac Development and Fertilization in ArabidopsisTraditionally considered to be deleterious molecules, reactive oxygen species (ROS) are emerging as essential signaling molecules in numerous organisms. Here, we show how ROS play a crucial role during female gametogenesis and fertilization in plants. Mitochondrial Mn-superoxide dismutase appears critical for maintaining ROS localization and important for embryo sac patterning.
Inactivation of Plasma Membrane–Localized CDPK-RELATED KINASE5 Decelerates PIN2 Exocytosis and Root Gravitropic Response in ArabidopsisThis work shows that CRK5, a plasma membrane–associated member of the Arabidopsis Ca2+/calmodulin-dependent kinase-related protein family, phosphorylates the hydrophilic loop of PIN2 and is required for proper polar localization of PIN2 in the transition zones of roots. Inactivation of CRK5 inhibits primary root elongation and delays gravitropic bending of roots and shoots.
MIXTA-Like Transcription Factors and WAX INDUCER1/SHINE1 Coordinately Regulate Cuticle Development in Arabidopsis and Torenia fournieriMIXTA-like MYB transcription factors MYB106 and MYB16, which are known to be involved in epidermal cell shaping, regulate accumulation of cuticular waxes and nanoridges, as revealed by employing Arabidopsis and wishbone flower as model systems. MYB106 positively regulates the expression of cuticle biosynthesis genes and another cuticle regulator, WIN1/SHN1 transcription factor, as well.
Seed Architecture Shapes Embryo Metabolism in Oilseed RapeThis work investigates how metabolism and oil storage capacity of the growing embryo of oilseed rape is adjusted to developmental changes in its architecture. It shows that locally distinct growth conditions due to the folding of cotyledons cause metabolic heterogeneity that reflects at the level of pathway activity, metabolites, and storage products (oil/protein).
A bHLH-Type Transcription Factor, ABA-INDUCIBLE BHLH-TYPE TRANSCRIPTION FACTOR/JA-ASSOCIATED MYC2-LIKE1, Acts as a Repressor to Negatively Regulate Jasmonate Signaling in ArabidopsisThis work identifies the bHLH transcription factor, JA-ASSOCIATED MYC2-LIKE1 (JAM1), which negatively regulates jasmonate responses independently from known regulators, namely, JASMONATE-ZIM DOMAIN proteins. JAM1 is involved in JA-mediated male fertility and the defense response to insect attack and represses the transcription of the target genes of MYC2 by competing for the binding sequences.
Antagonistic Basic Helix-Loop-Helix/bZIP Transcription Factors Form Transcriptional Modules That Integrate Light and Reactive Oxygen Species Signaling in ArabidopsisThis study shows that PIF1/PIF3 and HY5/HYH physically interact and coordinately regulate the expression of ROS-responsive genes. It reveals that the PIF1/PIF3-HY5/HYH transcriptional modules mediate crosstalk between light and ROS signaling pathways and suggests a mechanism by which plants optimize their growth in response to excess light.
D6PK AGCVIII Kinases Are Required for Auxin Transport and Phototropic Hypocotyl Bending in ArabidopsisThis work demonstrates that D6PK AGC kinases and PIN auxin transporters are required for phototropic hypocotyl bending. The findings suggest that D6PK-mediated phosphorylation of PIN transporters promotes auxin transport in the hypocotyl to ensure proper phototropic hypocotyl bending.
Increased Expression of a Phloem Membrane Protein Encoded by NHL26 Alters Phloem Export and Sugar Partitioning in ArabidopsisThis work examines plants overexpressing the putative membrane protein NDR1/HIN1-like 26 (NHL26), finding that overexpressor plants grew more slowly and accumulated more shoot biomass and leaf carbohydrates than wild-type plants. NHL26 localizes in the phloem plasmodesmata and endoplasmic reticulum, indicating a function in plasmodesmata permeability or sugar signaling in companion cells.
RICE SALT SENSITIVE3 Forms a Ternary Complex with JAZ and Class-C bHLH Factors and Regulates Jasmonate-Induced Gene Expression and Root Cell ElongationThis work shows that a novel nuclear factor, RICE SALT SENSITIVE3 (RSS3), interacts with and mediates the regulation of non-MYC-type bHLH transcription factors by interacting with JAZ proteins and thereby regulates the expression of jasmonate-responsive genes. RSS3 function is required for root cell elongation and the control of root growth under salinity conditions.
The α/β Hydrolase CGI-58 and Peroxisomal Transport Protein PXA1 Coregulate Lipid Homeostasis and Signaling in ArabidopsisArabidopsis CGI-58 influences multiple aspects of lipid metabolism by interacting with the peroxisomal transport protein PXA1. PXA1 serves as a gateway for the entry of lipids into peroxisomes, where additional enzymes are present for the degradation of fatty acids or the conversion of jasmonate and auxin precursors into biologically more active forms.
Light-Regulated Hypocotyl Elongation Involves Proteasome-Dependent Degradation of the Microtubule Regulatory Protein WDL3 in ArabidopsisMicrotubule regulatory proteins participate in the promotion of hypocotyl growth in darkness and inhibition of growth in light by altering microtubule organization in hypocotyl cells. Here, we show that a ubiquitin-26S proteasome–dependent mechanism regulates the levels of the microtubule regulatory protein WDL3 in response to light to modulate hypocotyl cell elongation in Arabidopsis.
Golgi Traffic and Integrity Depend on N-Myristoyl Transferase-1 in ArabidopsisA microscopy screen for endomembrane defects identified an Arabidopsis N-myristoyltransferase (NMT1) mutant exhibiting reduced activity of the expressed protein. Characterization of this mutant highlights a postembryonic role for NMT1 in the functional and morphological integrity of the Golgi predominantly challenging the Golgi membrane/cytosol partitioning of ADP-ribosylation factors.
EXO70A1-Mediated Vesicle Trafficking Is Critical for Tracheary Element Development in ArabidopsisGenes encoding for EXO70, a component of the exocyst complex, are highly expanded in plant genomes, with reasons unknown. EXO70A1 expressed primarily in tracheary elements regulates vesicle trafficking during xylem formation, suggesting that individual EXO70 members in plants may act in cell type– or cargo-specific exocytosis.
Chloroplast Division Protein ARC3 Regulates Chloroplast FtsZ-Ring Assembly and Positioning in Arabidopsis through Interaction with FtsZ2Symmetric division of chloroplasts ensures consistent chloroplast morphology during leaf growth and development. This study reveals that Arabidopsis ACCUMULATION AND REPLICATION OF CHLOROPLASTS3 negatively regulates chloroplast division-site placement in concert with MinD1 and MinE1 by inhibiting FtsZ ring assembly at nondivision sites primarily through interaction with FtsZ2.
Arabidopsis Villins Promote Actin Turnover at Pollen Tube Tips and Facilitate the Construction of Actin CollarsThis study determines the quantitative dynamic parameters associated with actin filament growth and disappearance at pollen tube tips and identifies villin as a key regulator of actin dynamics in this region. Real-time visualization of single filaments showing that villin regulates actin dynamics via its severing activity supports a direct link between villin and filament severing in plants.
Loss of Plastoglobule Kinases ABC1K1 and ABC1K3 Causes Conditional Degreening, Modified Prenyl-Lipids, and Recruitment of the Jasmonic Acid PathwayABC1K1 and ABC1K3, two of the six plastoglobule ABC1K kinases, physically interact, and the double mutant displays a conditional senescent-like phenotype. ABC1K1 and 3 regulate prenyl-lipid metabolism and phosphorylation targets likely include tocopherol cyclase, VTE1. Plastoglobules function as specialized thylakoid microdomains with local enrichment of selected proteins and metabolites.
ABCC1, an ATP Binding Cassette Protein from Grape Berry, Transports Anthocyanidin 3-O-GlucosidesThis work provides biochemical evidence that ABCC transporters are directly involved in anthocyanin transport into plant vacuoles. The presence of reduced glutathione is a prerequisite for the transport. Our data support that anthocyanins and glutathione are cotransported but that no glutathione anthocyanin conjugate is formed.
Silencing of the Nuclear RPS10 Gene Encoding Mitochondrial Ribosomal Protein Alters Translation in Arabidopsis MitochondriaThis work addresses both mitochondrial translation regulation and coordination of expression of nuclear and mitochondrial genomes in land plants. When the status of mitoribosomes is perturbed, the efficiency of translation of various classes of mitochondrial mRNAs is differently affected. In consequence, ribosomal proteins are oversynthesized, whereas OXPHOS subunits are downregulated.
Cytochrome P450 CYP89A9 Is Involved in the Formation of Major Chlorophyll Catabolites during Leaf Senescence in ArabidopsisThis work identifies dioxobilin-type catabolites to represent more than 90% of the chlorophyll breakdown products in Arabidopsis. Their formation from formyloxobilin-type precursors is catalyzed by CYP89A9 in an unusual oxidative deformylation reaction. Our findings reveal a transformation in the complex pathway of chlorophyll breakdown that may also occur in other plant species.
Abnormal Glycosphingolipid Mannosylation Triggers Salicylic Acid–Mediated Responses in ArabidopsisWe showed that a Golgi sugar nucleotide transporter (GONST1) is not required for polysaccharide biosynthesis as previously hypothesized. Instead, we found that GONST1 provides substrate for the glycosylation of an abundant class of sphingolipid. gonst1 plants are stunted and display a constitutive defense response, including elevated salicylic acid and hydrogen peroxide levels.
Deletion of a Tandem Gene Family in Arabidopsis: Increased MEKK2 Abundance Triggers Autoimmunity when the MEKK1-MKK1/2-MPK4 Signaling Cascade Is DisruptedThis work examines the MAP kinase cascade encoded by MEKK1, MKK1/MKK2, and MPK4, finding that deletion of the MEKK1/2/3 tandem gene family produces a wild-type plant and that the autoimmune phenotypes of mutants in this pathway require MEKK2. The key determinant of autoimmunity was found to be the level of MEKK2 expression, which was shown to be regulated by MPK4 activity.
