Table of Contents
IN BRIEF
LARGE-SCALE BIOLOGY ARTICLES
The High Polyphenol Content of Grapevine Cultivar Tannat Berries Is Conferred Primarily by Genes That Are Not Shared with the Reference GenomeThe Tannat grape berry is used to produce high-quality wines with an intense purple color and remarkable antioxidant properties. Through reference-guided assembly of the genome combined with de novo assembly of the transcriptome, we found that the variety-specific genes that might contribute substantially to the unique characteristics of the Tannat berry are not present in the reference genome.
Abscisic Acid–Responsive Guard Cell Metabolomes of Arabidopsis Wild-Type and gpa1 G-Protein MutantsThe authors performed metabolomics analysis on a time series of guard cell samples treated with abscisic acid (ABA) to follow the dynamics of 85 metabolites potentially involved in ABA signaling. ABA rapidly altered the profiles of numerous metabolites, including other hormones and calcium-mobilizing agents. ABA responses were greater in the wild type than in a G-protein mutant with ABA-hyposensitive stomata.
CAROTENOID CLEAVAGE DIOXYGENASE4 Is a Negative Regulator of β-Carotene Content in Arabidopsis SeedsAnalysis of natural variation in Arabidopsis identified CAROTENOID CLEAVAGE DIOXYGENASE4 (CCD4) as a major negative regulator of β-carotene content in seeds and senescing leaves. Given that global vitamin A deficiency is due in part to low β-carotene levels in seeds of major food crops, this study suggests that CCDs may be critical targets for enhancing the provitamin A carotenoid levels of food crops.
Genome-Wide Analysis of Branched-Chain Amino Acid Levels in Arabidopsis SeedsGenome-wide association studies of free branched-chain amino acids (BCAAs) in Arabidopsis seeds identified BRANCHED-CHAIN AMINO ACID TRANSFERASE2 (BCAT2), one of seven BCATs encoded in the genome, as an important regulator of BCAA natural variation. The mitochondrial localization of BCAT2 is consistent with a catabolic function and highlights the importance of catabolism in determining seed BCAA levels.
RESEARCH ARTICLES
The Trans-Acting Short Interfering RNA3 Pathway and NO APICAL MERISTEM Antagonistically Regulate Leaf Margin Development and Lateral Organ Separation, as Revealed by Analysis of an argonaute7/lobed leaflet1 Mutant in Medicago truncatulaThis work shows that a mutation of the ARGONAUTE7 ortholog (LOBED LEAFLET1) in Medicago truncatula causes lobed leaf margins and more widely spaced lateral organs. Characterization of the mutant revealed a balanced developmental mechanism involving several regulators that determine the final shape of leaf margin and the separation of lateral organs.
ABA-INSENSITIVE3, ABA-INSENSITIVE5, and DELLAs Interact to Activate the Expression of SOMNUS and Other High-Temperature-Inducible Genes in Imbibed Seeds in ArabidopsisThe Arabidopsis aba2, abi3, della pentuple, and som mutant seeds germinate even at high temperature. This work shows that ABI3, ABI5, and DELLA target to the SOM promoter and mediate high-temperature signaling to activate the expression of SOM in imbibed seeds.
Arabidopsis ERG28 Tethers the Sterol C4-Demethylation Complex to Prevent Accumulation of a Biosynthetic Intermediate That Interferes with Polar Auxin TransportSterol biosynthetic intermediates (SBIs) derived from the sterol C4-demethylation complex tethered by ERG28 represent signaling molecules in mammals and fungi. In Arabidopsis, loss of ERG28 function leads to the accumulation of the previously undetected SBI, 4-carboxy-4-methyl-24-methylenecycloartanol, which inhibits polar auxin transport. Our work provides a link between sterol metabolism and auxin transport.
Phosphatidylinositol 4,5-Bisphosphate Influences PIN Polarization by Controlling Clathrin-Mediated Membrane Trafficking in ArabidopsisPlant growth follows positional cues provided by the phytohormone auxin. A key determinant of auxin distribution is the asymmetric plasma membrane localization of PIN-auxin transporters, which involves complex endocytotic cycling. Endocytosis and PIN distribution require the regulatory phospholipid, PtdIns(4,5)P2, which is formed by PI4P 5-kinases that themselves display polarized distribution.
CELLULOSE SYNTHASE INTERACTIVE3 Regulates Cellulose Biosynthesis in Both a Microtubule-Dependent and Microtubule-Independent Manner in ArabidopsisCELLULOSE SYNTHASE INTERACTIVE3 (CSI3) is an important regulator of cellulose biosynthesis and anisotropic growth. Together with CSI1, CSI3 regulates the rate of cellulose biosynthesis in both a microtubule-dependent and microtubule-independent manner in Arabidopsis.
Sufficient Amounts of Functional HOP2/MND1 Complex Promote Interhomolog DNA Repair but Are Dispensable for Intersister DNA Repair during Meiosis in ArabidopsisThis article elucidates molecular details of meiotic DNA repair by analyzing the interhomolog-promoting factor HOP2. The study found that the recombinase DMC1 requires high levels of HOP2 for repair via the homologous chromosome but only minimal amounts to allow the recombinase RAD51 to perform intersister DNA repair, indicating that DMC1 exerts a negative regulatory effect on RAD51, which is alleviated by HOP2.
NAC Transcription Factor SPEEDY HYPONASTIC GROWTH Regulates Flooding-Induced Leaf Movement in ArabidopsisIn rosette plants, waterlogging triggers an upward (hyponastic) leaf movement that positions the photosynthetically active organs above the rising water level. This work reports the identification of a transcriptional regulator that affects this response by regulating the expression of its direct target gene, ACO5, encoding ACC oxidase, a key enzyme of ethylene biosynthesis.
Autophagy-Related Proteins Are Required for Degradation of Peroxisomes in Arabidopsis Hypocotyls during Seedling GrowthThis work reveals a function for autophagy in Arabidopsis hypocotyls after germination. By delivering peroxisomes and other cytoplasmic components to the lytic vacuole for degradation, autophagic machinery may help plant cells clean up old organelles for cell remodeling.
Highly Oxidized Peroxisomes Are Selectively Degraded via Autophagy in ArabidopsisPeroxisomes are organelles that generate reactive oxygen species such as hydrogen peroxide. This study shows that peroxisomes damaged by hydrogen peroxide are degraded via autophagy, suggesting that autophagy plays an important role in quality control of peroxisomes.
Arabidopsis Chlorophyll Biosynthesis: An Essential Balance between the Methylerythritol Phosphate and Tetrapyrrole PathwaysThis work provides evidence into how inhibition of the methylerythritol phosphate pathway causes plant death. Chlorophyll is composed of a chlorin ring, generated by the tetrapyrrole pathway, and an isoprenoid tail, made from the methylerythritol phosphate pathway. The data herein demonstrate that stoichiometric balance between these pathways is essential for viability.
Arabidopsis Kelch Repeat F-Box Proteins Regulate Phenylpropanoid Biosynthesis via Controlling the Turnover of Phenylalanine Ammonia-LyasePhenylalanine ammonia-lyase (PAL) catalyzes the first rate-limiting step in the phenylpropanoid pathway. Both in vitro and in vivo biochemical and genetic evidence demonstrated that a group of Kelch repeat F-box proteins physically interact with PAL isozymes, mediating their degradation via the ubiquitination-26S proteasome system, thus affecting phenylpropanoid biosynthesis.
Arabidopsis Phosphoglycerate Dehydrogenase1 of the Phosphoserine Pathway Is Essential for Development and Required for Ammonium Assimilation and Tryptophan BiosynthesisBiosynthesis of the amino acid serine occurs mainly via photorespiration in plants. This work shows, however, that locally restricted serine biosynthesis via the alternative phosphoserine pathway is required for proper embryo development and leaf initiation, highlighting the importance of cellular resolution when analyzing metabolic pathways.
Phosphatidic Acid Interacts with a MYB Transcription Factor and Regulates Its Nuclear Localization and Function in ArabidopsisPhosphatidic acid has emerged as a class of cellular mediators involved in various cellular and physiological processes. However, little is known about its mechanism of action. This study shows that phosphatidic acid binds to the MYB transcription factor WER and suggests that the interaction is necessary for the nuclear localization of WER and for WER-mediated regulation of root hair formation.
Characterization of Solanum tuberosum Multicystatin and the Significance of Core DomainsThis study characterizes the structure and significance of the core of potato multicystatin (PMC), a multidomain cysteine protease inhibitor found in the cortical parenchyma tissue of potato tubers. Papain inhibitory properties of native and recombinant PMC containing core domains are affected by pH. It is likely that pH-mediated regulation imparts unique properties to PMC that modulate proteolysis upon wounding and/or infection via inhibiting cysteine proteases.
Calcium/Calmodulin-Dependent Protein Kinase Is Negatively and Positively Regulated by Calcium, Providing a Mechanism for Decoding Calcium Responses during Symbiosis SignalingThis study dissects the regulation of a calcium/calmodulin-dependent protein kinase (CCaMK) during symbiotic signaling and reveals that CCaMK is both negatively and positively regulated by calcium to create a robust molecular switch that is responsive to calcium concentrations associated with both the basal state and with oscillations.
COMMENTARIES