Table of Contents
IN BRIEF
LETTERS TO THE EDITOR
REVIEWS
- The Emerging Importance of Type I MADS Box Transcription Factors for Plant Reproduction
Based on their evolutionary origin, MADS box transcription factor genes have been divided into two classes, namely, type I and II. The plant-specific type II MIKC MADS box genes have been most intensively studied and shown to be key regulators of developmental processes, such as meristem identity, flowering time, and fruit and seed development. By contrast, very little is known about type I MADS domain transcription factors, and they have not attracted interest for a long time. A number of recent studies have now indicated a key regulatory role for type I MADS box factors in plant reproduction, in particular in specifying female gametophyte, embryo, and endosperm development. These analyses have also suggested that type I MADS box factors are decisive for setting reproductive boundaries between species.
LARGE-SCALE BIOLOGY ARTICLES
- High-Resolution Temporal Profiling of Transcripts during Arabidopsis Leaf Senescence Reveals a Distinct Chronology of Processes and Regulation
This work presents a high-resolution time-course analysis of gene expression during development of a leaf from expansion through senescence. Enrichment in ontologies, sequence motifs, and transcription factor families within genes showing altered expression over time identified both metabolic pathways and potential regulators active at different stages of leaf development and senescence.
- PlaNet: Combined Sequence and Expression Comparisons across Plant Networks Derived from Seven Species
Genes that are similarly expressed, or coexpressed, are often involved in related biological processes. Such coexpressed relationships also appear to be conserved across species. The PlaNet platform enables comparative analysis of genome-wide coexpression networks across seven plant species, thus enabling prediction of gene function and elucidation of the identity of functional homologs.
- The Predicted Arabidopsis Interactome Resource and Network Topology-Based Systems Biology Analyses
Protein–protein interactions are important mechanisms for genes and gene networks to function. This study demonstrates that, although the PAIR database has limited coverage, representing ~24% of the entire interactome with ~40% precision, it is rich enough to capture many significant functional linkages within and between higher-order biological systems, such as pathways and biological processes.
RESEARCH ARTICLES
- Transcriptome and Metabolite Profiling Show That APETALA2a Is a Major Regulator of Tomato Fruit Ripening
This study demonstrates that the tomato APETALA2a (AP2a) transcription factor modulates fruit ripening by negatively regulating ethylene biosynthesis and signaling. Various ripening regulators are shown to act upstream of AP2a. Gene expression analysis reveals that AP2a is involved in chloroplast to chromoplast transition.
- The FT-Like ZCN8 Gene Functions as a Floral Activator and Is Involved in Photoperiod Sensitivity in Maize
The transition from vegetative to reproductive development is regulated by the activity of graft-transmissible flowering hormone, florigen, which is encoded by the FLOWERING LOCUS T (FT) family of mobile proteins. This work identified, among many maize FT-like genes, a single gene, ZCN8, which has all required characteristics to function as florigen.
- BROTHER OF LUX ARRHYTHMO Is a Component of the Arabidopsis Circadian Clock
This work shows that the Arabidopsis transcription factor BROTHER OF LUX ARRHYTHMO (BOA) is an activator in regulating the expression of CIRCADIAN CLOCK ASSOCIATED1 (CCA1). BOA forms a transcriptional feedback loop with CCA1 and regulates circadian rhythms in Arabidopsis.
- AUXIN RESPONSE FACTOR8 Regulates Arabidopsis Petal Growth by Interacting with the bHLH Transcription Factor BIGPETALp
This study defines a previously unknown combinatorial interaction between transcription factors in plants and provides a better understanding of how plants integrate signals to regulate petal development. It also highlights the role of a motif in the bHLH transcription factor that resembles a motif that was previously shown to be important in auxin signaling.
- Multiple Facets of Arabidopsis Seedling Development Require Indole-3-Butyric Acid–Derived Auxin
Plants synthesize the growth hormone indole-3-acetic acid using a variety of incompletely understood pathways. This work demonstrates that the conversion of indole-3-butyric acid to indole-3-acetic acid contributes to wide-ranging auxin-regulated processes in Arabidopsis seedlings and that shutting off this auxin supply renders seedlings less able to respond to exogenous auxin.
- The Jasmonate-ZIM Domain Proteins Interact with the R2R3-MYB Transcription Factors MYB21 and MYB24 to Affect Jasmonate-Regulated Stamen Development in Arabidopsis
Jasmonate is essential for diverse biological processes, including male fertility and plant defense in Arabidopsis. This work shows that the R2R3-MYB transcription factors MYB21 and MYB24 function as direct targets of JAZ proteins to mediate jasmonate-regulated stamen development.
- Geminiviruses Subvert Ubiquitination by Altering CSN-Mediated Derubylation of SCF E3 Ligase Complexes and Inhibit Jasmonate Signaling in Arabidopsis thaliana
This study shows that geminivirus C2/L2 protein interferes with the derubylation of CUL1. Responses regulated by the CUL1-based SCF ubiquitin ligases, and particularly the response to jasmonates, are altered in transgenic Arabidopsis thaliana expressing C2/L2. The capability to selectively interfere with SCF complexes may define a novel and powerful strategy in viral infections.
- The Anaphase-Promoting Complex Is a Dual Integrator That Regulates Both MicroRNA-Mediated Transcriptional Regulation of Cyclin B1 and Degradation of Cyclin B1 during Arabidopsis Male Gametophyte Development
This study shows that, in addition to its known role in protein degradation, the anaphase-promoting complex also regulates transcription of a cell cycle gene, Cyclin B1, and that this regulation, which is mediated by microRNA, is important for pollen development.
- The CHD3 Chromatin Remodeler PICKLE and Polycomb Group Proteins Antagonistically Regulate Meristem Activity in the Arabidopsis Root
We report that the chromatin remodeling factor PICKLE and Polycomb group proteins antagonistically determine cell identity. Our study highlights an important role of PICKLE and Polycomb group proteins in regulating root meristem activity by regulating the expression of root stem cell and meristem marker genes.
- Sphingolipids in the Root Play an Important Role in Regulating the Leaf Ionome in Arabidopsis thaliana
Sphingolipids are a diverse group of essential membrane lipids thought to play important roles in both membrane function and cellular signaling. By identifying an Arabidopsis thaliana mutant lacking 3-ketodihydrosphinganine reductase, a critical enzyme in sphingolipid biosynthesis, this work uncovers a connection between sphingolipid metabolism in roots and whole-plant mineral ion homeostasis.
- APO1 Promotes the Splicing of Chloroplast Group II Introns and Harbors a Plant-Specific Zinc-Dependent RNA Binding Domain
This study demonstrates that APO1, originally proposed to be involved in the maturation of proteins with [4Fe-4S] ligands, is instead required for the splicing of several chloroplast introns. It shows further that DUF794, the plant-specific domain of unknown function that makes up the bulk of APO1, is an RNA binding domain harboring zinc binding motifs.
- Arabidopsis Kinesin KP1 Specifically Interacts with VDAC3, a Mitochondrial Protein, and Regulates Respiration during Seed Germination at Low Temperature
A plant-specific molecular motor (KP1) specifically interacts with a channel protein (VDAC3) of the mitochondrial outer membrane and is targeted to mitochondria via its tail domain. In seedlings germinated at 4°C, either mutant of the two genes exhibited increased oxygen consumption, respiration imbalance, and reduced ATP levels.
- Patatin-Related Phospholipase pPLAIIIβ-Induced Changes in Lipid Metabolism Alter Cellulose Content and Cell Elongation in Arabidopsis
Patatin-related phospholipase pPLAIIIβ lacks the canonical esterase catalytic center but possesses acyl-hydrolyzing and acyl-CoA thioesterase activities. Knockout and overexpression of pPLAIIIβ have opposite effects on the levels of membrane lipids, cellulose content, mechanical strength, and cell length. Thus, membrane lipid metabolism may be linked to cellulose production in Arabidopsis.
- Disruption of LACCASE4 and 17 Results in Tissue-Specific Alterations to Lignification of Arabidopsis thaliana Stems
This study provides evidence that two laccases, LAC4 and LAC17, participate in the polymerization of lignins in Arabidopsis stems. These findings suggest that the genetic engineering of lignin-specific laccases is a potentially innovative and promising tool for the fine-tuning of lignin content and structure.
- The MYB96 Transcription Factor Regulates Cuticular Wax Biosynthesis under Drought Conditions in Arabidopsis
This work provides evidence that deposition of cuticular waxes is intimately associated with plant responses to drought. The Arabidopsis MYB96 transcription factor functions as a regulator of ABA-mediated cuticular wax biosynthesis under drought conditions by binding directly to the promoters of genes encoding very-long-chain fatty acid–condensing enzymes involved in cuticular wax biosynthesis.
- Phosphorylation of the Nicotiana benthamiana WRKY8 Transcription Factor by MAPK Functions in the Defense Response
This study identified WRKY8 as a downstream target of three mitogen-activated protein kinases in Nicotiana benthamiana. Phosphorylation of WRKY8 increased its DNA binding activity, and ectopic expression of WRKY8 induced the expression of various defense-related genes.
- The Membrane Mucin Msb2 Regulates Invasive Growth and Plant Infection in Fusarium oxysporum
This study examines the activation of a conserved mitogen-activated protein kinase (MAPK) cascade that is essential for fungal pathogenicity in plants. A highly glycosylated mucin-like transmembrane protein is shown to contribute to phosphorylation of the MAPK that promotes invasive growth and virulence in the soilborne vascular wilt fungus Fusarium oxysporum.
COMMENTARY