Plant Biology*

The 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.

At 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.

Plant 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.