Plant Biology
The two paralogous kiwellin proteins KWL1 and KWL1-b from maize are structurally related and have overlapping functions in plant defense
Many plant-pathogenic bacteria and fungi deploy effector proteins that down-regulate plant defense responses and reprogram plant metabolism for colonization and survival in planta. Kiwellin (KWL) proteins are a widespread family of plant-defense proteins that target these microbial effectors. The KWL1 protein from maize (corn, Zea mays) specifically inhibits the enzymatic activity of the secreted chorismate mutase Cmu1, a virulence-promoting effector of the smut fungus Ustilago maydis. In addition to KWL1, 19 additional KWL paralogs have been identified in maize.Impaired folate binding of serine hydroxymethyltransferase 8 from soybean underlies resistance to the soybean cyst nematode
Management of the agricultural pathogen soybean cyst nematode (SCN) relies on the use of SCN-resistant soybean cultivars, a strategy that has been failing in recent years. An underutilized source of resistance in the soybean genotype Peking is linked to two polymorphisms in serine hydroxy-methyltransferase 8 (SHMT8). SHMT is a pyridoxal 5′-phosphate–dependent enzyme that converts l-serine and (6S)-tetrahydrofolate to glycine and 5,10-methylenetetrahydrofolate. Here, we determined five crystal structures of the 1884-residue SHMT8 tetramers from the SCN-susceptible cultivar (cv.) Essex and the SCN-resistant cv.Brassicaceae-specific Gretchen Hagen 3 acyl acid amido synthetases conjugate amino acids to chorismate, a precursor of aromatic amino acids and salicylic acid
To modulate responses to developmental or environmental cues, plants use Gretchen Hagen 3 (GH3) acyl acid amido synthetases to conjugate an amino acid to a plant hormone, a reaction that regulates free hormone concentration and downstream responses. The model plant Arabidopsis thaliana has 19 GH3 proteins, of which 8 have confirmed biochemical functions. One Brassicaceae-specific clade of GH3 proteins was predicted to use benzoate as a substrate and includes AtGH3.7 and AtGH3.12/PBS3. Previously identified as a 4-hydroxybenzoic acid-glutamate synthetase, AtGH3.12/PBS3 influences pathogen defense responses through salicylic acid.An aldo-keto reductase with 2-keto-l-gulonate reductase activity functions in l-tartaric acid biosynthesis from vitamin C in Vitis vinifera
Tartaric acid has high economic value as an antioxidant and flavorant in food and wine industries. l-Tartaric acid biosynthesis in wine grape (Vitis vinifera) uses ascorbic acid (vitamin C) as precursor, representing an unusual metabolic fate for ascorbic acid degradation. Reduction of the ascorbate breakdown product 2-keto-l-gulonic acid to l-idonic acid constitutes a critical step in this l-tartaric acid biosynthetic pathway. However, the underlying enzymatic mechanisms remain obscure. Here, we identified a V.Structure–function studies of tetrahydroprotoberberine N-methyltransferase reveal the molecular basis of stereoselective substrate recognition
Benzylisoquinoline alkaloids (BIAs) are a structurally diverse class of plant-specialized metabolites that have been particularly well-studied in the order Ranunculales. The N-methyltransferases (NMTs) in BIA biosynthesis can be divided into three groups according to substrate specificity and amino acid sequence. Here, we report the first crystal structures of enzyme complexes from the tetrahydroprotoberberine NMT (TNMT) subclass, specifically for GfTNMT from the yellow horned poppy (Glaucium flavum).Arabidopsis thaliana GH3.15 acyl acid amido synthetase has a highly specific substrate preference for the auxin precursor indole-3-butyric acid
Various phytohormones control plant growth and development and mediate biotic and abiotic stress responses. Gretchen Hagen 3 (GH3) acyl acid amido synthetases are plant enzymes that typically conjugate amino acids to indole-3-acetic acid (IAA) or jasmonic acid (JA) to inactivate or activate these phytohormones, respectively; however, the physiological and biological roles of many of these enzymes remain unclear. Using a biochemical approach, we found that the Arabidopsis thaliana GH3.15 (AtGH3.15) preferentially uses indole-3-butyric acid (IBA) and glutamine as substrates.Covering their bases: The phosphobase methylation pathway in plants
Phosphoethanolamine methyltransferases add three methyl groups successively to their substrate to produce phosphocholine, an important precursor for phospholipid biosynthesis in diverse organisms. New work from Lee and Jez reveals critical domain movements that explain how multiple methylation reactions are uniquely coordinated by plant methyltransferases and provides insights into the evolution of this class of enzymes. As opposed to closely related family members, the intermediates in this pathway are likely shuttled between two tethered domains to ensure complete methylation.Conformational changes in the di-domain structure of Arabidopsis phosphoethanolamine methyltransferase leads to active-site formation
Phosphocholine (pCho) is a precursor for phosphatidylcholine and osmoprotectants in plants. In plants, de novo synthesis of pCho relies on the phosphobase methylation pathway. Phosphoethanolamine methyltransferase (PMT) catalyzes the triple methylation of phosphoethanolamine (pEA) to pCho. The plant PMTs are di-domain methyltransferases that divide the methylation of pEA in one domain from subsequent methylations in the second domain. To understand the molecular basis of this architecture, we examined the biochemical properties of three Arabidopsis thaliana PMTs (AtPMT1–3) and determined the X-ray crystal structures of AtPMT1 and AtPMT2.Conformational dynamics are a key factor in signaling mediated by the receiver domain of a sensor histidine kinase from Arabidopsis thaliana
Multistep phosphorelay (MSP) cascades mediate responses to a wide spectrum of stimuli, including plant hormonal signaling, but several aspects of MSP await elucidation. Here, we provide first insight into the key step of MSP-mediated phosphotransfer in a eukaryotic system, the phosphorylation of the receiver domain of the histidine kinase CYTOKININ-INDEPENDENT 1 (CKI1RD) from Arabidopsis thaliana. We observed that the crystal structures of free, Mg2+-bound, and beryllofluoridated CKI1RD (a stable analogue of the labile phosphorylated form) were identical and similar to the active state of receiver domains of bacterial response regulators.
