The Arabidopsis protein phosphatase PP2C38 negatively regulates the central immune kinase BIK1

Plants recognize pathogen-associated molecular patterns (PAMPs) via cell surface-localized pattern recognition receptors (PRRs), leading to PRR-triggered immunity (PTI). The Arabidopsis cytoplasmic kinase BIK1 is a downstream substrate of several PRR complexes. How plant PTI is negatively regulated is not fully understood. Here, we identify the protein phosphatase PP2C38 as a negative regulator of BIK1 activity and BIK1-mediated immunity. PP2C38 dynamically associates with BIK1, as well as with the PRRs FLS2 and EFR, but not with the co-receptor BAK1. PP2C38 regulates PAMP-induced BIK1 phosphorylation and impairs the phosphorylation of the NADPH oxidase RBOHD by BIK1, leading to reduced oxidative burst and stomatal immunity. Upon PAMP perception, PP2C38 is phosphorylated on serine 77 and dissociates from the FLS2/EFR-BIK1 complexes, enabling full BIK1 activation. Together with our recent work on the control of BIK1 turnover, this study reveals another important regulatory mechanism of this central immune component

Argyrin B a non-competitive inhibitor of the human immunoproteasome exhibiting preference for β1i

Inhibitors of the proteasome have found broad therapeutic applications however, they show severe toxicity due to the abundance of proteasomes in healthy cells. In contrast, inhibitors of the immunoproteasome, which is upregulated during disease states, are less toxic and have increased therapeutic potential including against autoimmune disorders. In this project, we report argyrin B, a natural product cyclic peptide to be a reversible, non-competitive inhibitor of the immunoproteasome. Argyrin B showed selective inhibition of the β5i and β1i sites of the immunoproteasome over the β5c and β1c sites of the constitutive proteasome with nearly 20-fold selective inhibition of β1i over the homologous β1c. Molecular modelling attributes the β1i over β1c selectivity to the small hydrophobic S1 pocket of β1i and β5i over β5c to site-specific amino acid variations that enable additional bonding interactions and stabilization of the binding conformation. These findings facilitate the design of immunoproteasome selective and reversible inhibitors that may have a greater therapeutic potential and lower toxicity

Calcium-dependent protein kinase/NADPH oxidase activation circuit is required for rapid defense signal propagation

In animals and plants, pathogen recognition triggers the local activation of intracellular signaling that is prerequisite for mounting systemic defenses in the whole organism. We identified that Arabidopsis thaliana isoform CPK5 of the plant calcium-dependent protein kinase family becomes rapidly biochemically activated in response to pathogen-associated molecular pattern (PAMP) stimulation. CPK5 signaling resulted in enhanced salicylic acid–mediated resistance to the bacterial pathogen Pst DC3000, differential plant defense gene expression, and synthesis of reactive oxygen species (ROS). Using selected reaction monitoring MS, we identified the plant NADPH oxidase, respiratory burst oxidase homolog D (RBOHD), as an in vivo phosphorylation target of CPK5. Remarkably, CPK5-dependent in vivo phosphorylation of RBOHD occurs on both PAMP- and ROS stimulation. Furthermore, rapid CPK5-dependent biochemical and transcriptional activation of defense reactions at distal sites is compromised in cpk5 and rbohd mutants. Our data not only identify CPK5 as a key regulator of innate immune responses in plants but also support a model of ROS-mediated cell-to-cell communication, where a self-propagating mutual activation circuit consisting of the protein kinase, CPK5, and the NADPH oxidase RBOHD facilitates rapid signal propagation as a prerequisite for defense response activation at distal sites within the plant

Incidence of Juvenile Osteochondral Conditions in Thoroughbred Weanlings in the South of Brazil

The goal of this study was to determine the occurrence of juvenile osteochondral conditions (JOCCs) in Brazilian Thoroughbred weanlings from 4 to 6 months of age. Eighty-five foals from four different stud farms were evaluated. The history and husbandry of all animals were obtained by questionnaire, and clinical examination was performed to detect lameness. Radiographic evaluations included 24 radiographic projections from eight different joints (right and left metacarpophalangeal, metatarsophalangeal, tarsocrural, and femorotibial [FT] joints), for a total of 2,040 radiographs. Twenty locations within those joints were examined, and a severity index (SI) was determined for each location. The sum of the SI values for each foal was used to determine the osteoarticular status (OAS), which was classified as good, intermediate, or poor. None of the 85 foals examined had clinical signs of lameness. Sixty-five (76.5%) foals had one or more findings related to JOCC. In total, 680 joints were examined and scored, with 20.7% affected. The FT joints were the most commonly affected (n = 62; 9.1%). There was no significant difference in JOCC occurrence between the left and right limbs. The OAS was considered good in 38.8% (n = 33) of the foals studied, intermediate in 48.2% (n = 41), and poor in 12.9% (n = 11). There were significant differences in OAS among the four stud farms