Biology subjects

Schumacher, K.

Publications and source records attributed to Schumacher, K..

23 records · Page 2Linked to original sources

bioRxiv2019

Pathogen-induced pH changes regulate the growth-defense balance of plants

Environmental adaptation of organisms relies on fast perception and response to external signals, which lead to developmental changes. Plant cell growth is strongly dependent on cell wall remodeling. However, little is known about cell wall-related sensing of biotic stimuli and the downstream mechanisms that coordinate growth and defense responses. We generated genetically encoded pH sensors to determine absolute pH changes across the plasma membrane in response to biotic stress. A rapid apoplastic acidification by phosphorylation-based proton pump activation was followed by an acidification of the cortical side of the plasma membrane in response to the fungus Fusarium oxysporum. The proton chemical gradient modulation immediately reduced cellulose synthesis and cell growth and, furthermore, had a direct influence on the pathogenicity of the fungus. All these effects were dependent on the COMPANION OF CELLULOSE SYNTHASE proteins that are thus at the nexus of plant growth and defense. Hence, our discoveries show a remarkable connection between plant biomass production, immunity, and pH control, and advance our ability to investigate the plant growth-defense balance.

plant biology↗

bioRxiv2018

Pyrophosphate modulates stress responses via SUMOylation

Pyrophosphate (PPi), a byproduct of macromolecule biosynthesis is maintained at low levels by soluble inorganic pyrophosphatases (sPPase) found in all eukaryotes. In plants, H+-pumping pyrophosphatases (H+-PPase) convert the substantial energy present in PPi into an electrochemical gradient. We show here, that both cold- and heat stress sensitivity of fugu5 mutants lacking the major H+-PPase isoform AVP1 is caused by reduced SUMOylation. In addition, we show that increased PPi concentrations interfere with SUMOylation in yeast and we provide evidence that SUMO activating E1-enzymes are inhibited by micromolar concentrations of PPi in a non-competitive manner. Taken together, our results do not only provide a mechanistic explanation for the beneficial effects of AVP1 overexpression in plants but they also highlight PPi as an important integrator of metabolism and stress tolerance.

biochemistry↗

bioRxiv2018

Subtilase-mediated activation of CLEL peptides involves several processing events in consecutive compartments of the secretory pathway

Post-translationally modified peptides are involved in many aspects of plant growth and development. The maturation of these peptides from their larger precursors is still poorly understood. We show here that the biogenesis of CLEL6 and CLEL9 peptides in Arabidopsis thaliana requires a series of processing events in consecutive compartments of the secretory pathway. Following cleavage of the signal peptide upon entry into the endoplasmic reticulum (ER), the peptide precursors are processed in the cis-Golgi by the subtilase SBT6.1. SBT6.1-mediated cleavage within the variable domain allows for continued passage of the partially processed precursors through the secretory pathway, and is a prerequisite for subsequent post-translational modifications including tyrosine sulfation and proline hydroxylation within, and proteolytic maturation after exit from the Golgi. Activation by subtilase SBT3.8 in post-Golgi compartments depends on the N-terminal aspartate of the mature peptides. Our work highlights the complexity of post-translational precursor maturation allowing for stringent control of peptide biogenesis.

plant biology↗

bioRxiv2018

NHX-type Na+(K+)/H+ antiporter activity is required for endomembrane trafficking and ion homeostasis in Arabidopsis thaliana

The regulation of ion and pH homeostasis of endomembrane organelles is critical for functional protein trafficking, sorting and modification in eukaryotic cells. pH homeostasis is maintained through the activity of vacuolar H+-ATPases (V-ATPases) pumping protons (H+) into the endomembrane lumen, and counter-action by cation/proton exchangers such as the NHX family of Na+(K+)/H+ exchangers. In plants, disturbing V-ATPase activity at the trans-Golgi network/early endosome (TGN/EE) impairs secretory and endocytic trafficking. However, it is unclear if the endosomal NHX-type antiporters NHX5 and NHX6 play functionally similar roles in endomembrane trafficking through maintaining ion and pH homeostasis. Here we show through genetic, pharmacological, and live-cell imaging approaches that double knockout of endosomal isoforms NHX5 and NHX6 results in impairment of endosome motility, protein recycling at the TGN/EE, but not in the secretion of integral membrane proteins. Furthermore, we report that nhx5 nhx6 mutants are partially insensitive to osmotic swelling of TGN/EE induced by the monovalent cation ionophore monensin. Similarly, nhx5 nhx6 cells are unresponsive to late endosomal swelling by the phosphatidylinositol 3/4-kinase inhibitor wortmannin, demonstrating that NHX5 and NHX6 are required for maintaining endosomal cation balance. Lastly, we report that the distal region of the cytosolic tail of NHX6 is required for mediating NHX6 localisation to late endosomes, but does not appear to be essential for NHX6 function.

plant biology↗

bioRxiv2018

Fine-tuning of ABA responses by the protein kinase WNK8

The phytohormone abscisic acid (ABA) regulates various growth- and developmental processes in response to limiting water conditions. ABA functions through an established signaling pathway consisting of PYR1/PYL/RCAR ABA receptors that inhibit group A type 2C protein phosphatases (PP2Cs) in an ABA-dependent manner. Inhibition of PP2Cs enables the activation of SnRK2-type protein kinases that phosphorylate downstream targets including transcription factors and ion channels. However, ABA-dependent signals have to be integrated into other growth- and developmental programs to ensure a successful life cycle. Here, we have characterized the role of the protein kinase WNK8 in the ABA signalling pathway. Two T-DNA insertion alleles wnk8-1 and wnk8-4 exhibited contrasting ABA responses during seed germination and young seedling growth. However, reciprocal crossings with wild type plants suggested that wnk8-1 that still expressed the WNK8 kinase domain functioned in a hypermorphic and dominant manner. WNK8 directly interacted with the PP2C PP2CA in planta and was negatively regulated by this phosphatase in vitro. WNK8 also phosphorylated the ABA receptor PYR1 in vitro. Double mutant analyses revealed that the dominant allele wnk8-1 suppressed the ABA- and glucose hypersensitivity of the pp2ca-1 T-DNA allele. In transient protoplast assays WNK8 suppressed ABA-induced reporter gene expression that was dependent on a functional kinase. In summary, we have identified the protein kinase WNK8 as a negative regulator of ABA responses during young seedling establishment through its direct interaction with core ABA signaling components.\n\nSIGNIFICANCE STATEMENTThe phytohormone abscisic acid regulates the water household of plants through a defined core signaling pathway. Here we have identified the protein kinase WNK8 as a direct interactor of core abscisic acid signalling components and as a negative modulator of abscisic acid responses during young seedling development in Arabidopsis.

plant biology↗