Plant Biology*
The Systemin Signaling Cascade As Derived from Time Course Analyses of the Systemin-responsive PhosphoproteomeThe early phosphorylation signaling cascade of the peptide hormone systemin was defined through comparing systemin-induced responses with non-specific responses induced by the inactive analogon systemin-A17 or mock treatment. Systemin-responsive phosphorylation of kinases and phosphatases was identified over a time course of 2 to 45 minutes, as well as typical substrate phosphorylation sites. We identified the C-terminal threonine of H+-ATPase LHA1 as a substrate of phosphatase PLL5 and MAP-Kinase MPK2, thereby defining a signaling circuit of rapid dephosphorylation and re-phosphorylation after 15 minutes.
Sucrose-induced Receptor Kinase 1 is Modulated by an Interacting Kinase with Short Extracellular DomainThe activation of aquaporins by a receptor kinase complex of SIRK1 and QSK1 was studied in detail. Based on phosphoproteomics, pulldown studies and physiological experiments we conclude that SIRK1 may function as a main receptor which forms a complex with coreceptor QSK1. SIRK1 can autophosphorylate and then trans-phosphorylate QSK1. Phosphorylated QSK1 enhanced and stabilized the interaction with aquaporins as substrates of the receptor kinase complex.
A Label-free Mass Spectrometry Method to Predict Endogenous Protein Complex CompositionAt least one third of soluble proteins are predicted to exist in a stable oligomeric state. However, the compositions of the vast majority are unknown. This paper describes a biochemical method to predict protein complex composition based on orthogonal chromatographic separations and label-free protein correlation profiling. The validated method predicts hundreds of novel homo- and heterooligomeric complexes, and provides a new way to analyze protein complexes in any organism with a well-annotated proteome.
Unraveling Hidden Components of the Chloroplast Envelope Proteome: Opportunities and Limits of Better MS SensitivityBy quantitatively comparing the proteomes of total leaf (crude cell extract) from Arabidopsis and purified chloroplast envelope fractions, this study makes available a novel parameter (calculated Enrichment Factor) for each putative envelope protein. This parameter provides important information to enable the more confident identification of genuine envelope components, distinguishing them from contaminants from other cellular/chloroplast compartments.
Complexome Profiling Reveals Association of PPR Proteins with Ribosomes in the Mitochondria of PlantsPlant mitochondrial protein expression is complex and routinely involves pentatricopeptide repeat proteins for processing of transcripts. Although the composition and structure of the mitoribosomes in other eukaryotic kingdoms of life is well established, plant mitochondria have so far eluded a detailed analysis. Using a complexome profiling approach, this study provides an early glimpse on the composition of plant mitochondrial ribosomes and sheds new light on the process of mitochondrial gene expression in plants. Mitochondrial subunits were found to possess several additional proteins carrying pentatricopeptide repeats potentially involved in RNA editing. Other proteins are potentially involved in the processing of nascent proteins.
Quantitative Early Auxin Root Proteomics Identifies GAUT10, a Galacturonosyltransferase, as a Novel Regulator of Root Meristem MaintenanceAuxin induces rapid abundance changes in various signaling proteins, transcriptional regulators, and enzymes such as cell wall modification proteins in roots. Loss of function of 15 top responsive proteins results in altered root phenotypes, demonstrating the power of this approach for reverse genetics screens. Characterization of the auxin responsive protein galacturonosyltransferase 10 demonstrates that this enzyme positively regulates sugar-mediated root meristem maintenance. Novel targeted proteomics assays demonstrate that all six auxin receptors remain stable in response to hormone.