StPIP1, a PAMP-induced peptide in potato, elicits plant defenses and is associated with disease symptom severity in a compatible interaction with Potato virus Y.

The role of small secreted peptides in plant defense responses to viruses has seldom been investigated. Here, we report a role for potato (Solanum tuberosum) PIP1, a gene predicted to encode a member of the pathogen-associated molecular pattern (PAMP)-induced peptide (PIP) family, in the response of potato to Potato virus Y (PVY) infection. We show that exogenous application of synthetic StPIP1 to potato leaves and nodes increased the production of reactive oxygen species and the expression of plant defense-related genes, revealing that StPIP1 triggers early defense responses. In support of this hypothesis, transgenic potato plants that constitutively overexpress StPIP1 had higher levels of leaf callose deposition and, based on measurements of viral RNA titers, were less susceptible to infection by a compatible PVY strain. Interestingly, systemic infection of StPIP1-overexpressing lines with PVY resulted in clear rugose mosaic symptoms that were absent or very mild in infected non-transgenic plants. A transcriptomics analysis revealed that marker genes associated with both pattern-triggered immunity and effector-triggered immunity were induced in infected StPIP1 overexpressors but not in non-transgenic plants. Together, our results reveal a role for StPIP1 in eliciting plant defense responses and in regulating plant antiviral immunity.

Analysis of formin functions during cytokinesis using specific inhibitor SMIFH2.

The phragmoplast separates daughter cells during cytokinesis by constructing the cell plate, which depends on interaction between cytoskeleton and membrane compartments. Proteins responsible for these interactions remain unknown, but formins can link cytoskeleton with membranes and several members of formin protein family localize to the cell plate. Progress in functional characterization of formins in cytokinesis is hindered by functional redundancies within the large formin gene family. We addressed this limitation by employing Small Molecular Inhibitor of Formin Homology 2 (SMIFH2), a small-molecule inhibitor of formins. Treatment of tobacco (Nicotiana tabacum) tissue culture cells with SMIFH2 perturbed localization of actin at the cell plate; slowed down both microtubule polymerization and phragmoplast expansion; diminished association of dynamin-related proteins with the cell plate independently of actin and microtubules; and caused cell plate swelling. Another impact of SMIFH2 was shortening of the END BINDING1b (EB1b) and EB1c comets on the growing microtubule plus ends in N. tabacum tissue culture cells and Arabidopsis thaliana cotyledon epidermis cells. The shape of the EB1 comets in the SMIFH2-treated cells resembled that of the knockdown mutant of plant Xenopus Microtubule-Associated protein of 215 kDa (XMAP215) homolog MICROTUBULE ORGANIZATION 1/GEMINI 1 (MOR1/GEM1). This outcome suggests that formins promote elongation of tubulin flares on the growing plus ends. Formins AtFH1 (A. thaliana Formin Homology 1) and AtFH8 can also interact with EB1. Besides cytokinesis, formins function in the mitotic spindle assembly and metaphase to anaphase transition. Our data suggest that during cytokinesis formins function in: (1) promoting microtubule polymerization; (2) nucleating F-actin at the cell plate; (3) retaining dynamin-related proteins at the cell plate; and (4) remodeling of the cell plate membrane.

Role of tropomodulin's leucine rich repeat domain in the formation of neurite-like processes.

Actin dynamics is fundamental for neurite development; monomer depolymerization from pointed ends is rate-limiting in actin treadmilling. Tropomodulins (Tmod) make up a family of actin pointed end-capping proteins. Of the four known isoforms, Tmod1-Tmod3 are expressed in brain cells. We investigated the role of Tmod's C-terminal (LRR) domain in the formation of neurite-like processes by overexpressing Tmod1 and Tmod2 with deleted or mutated LRR domains in PC12 cells, a model system used to study neuritogenesis. Tmod1 overexpression results in a normal quantity and a normal length of processes, while Tmod2 overexpression reduces both measures. The Tmod2 overexpression phenotype is mimicked by overexpression of Tmod1 with the LRR domain removed or with three point mutations in the LRR domain that disrupt exposed clusters of conserved residues. Removal of Tmod2's LRR domain does not significantly alter the outgrowth of neurite-like processes compared to that of Tmod2. Overexpression of chimeras with the N-terminal and C-terminal domains switched between Tmod1 and Tmod2 reinforces the idea that Tmod1's LRR domain counteracts the reductive effect of the Tmod N-terminal domain upon formation of processes while Tmod2's LRR domain does not. We suggest that the TM-dependent actin capping ability of both Tmods inhibits the formation of processes, but in Tmod1, this inhibition can be controlled via its LRR domain. Circular dichroism, limited proteolysis, and molecular dynamics demonstrate structural differences in the C-terminal region of the LRR domains of Tmod1, Tmod2, and the Tmod1 mutant.

Utilization of an in vivo reporter for high throughput identification of branched small molecule regulators of hypoxic adaptation.

Small molecules inhibiting hypoxia inducible factor (HIF) prolyl hydroxylases (PHDs) are the focus of drug development efforts directed toward the treatment of ischemia and metabolic imbalance. A cell-based reporter produced by fusing HIF-1 alpha oxygen degradable domain (ODD) to luciferase was shown to work as a capture assay monitoring stability of the overexpressed luciferase-labeled HIF PHD substrate under conditions more physiological than in vitro test tubes. High throughput screening identified novel catechol and oxyquinoline pharmacophores with a "branching motif" immediately adjacent to a Fe-binding motif that fits selectively into the HIF PHD active site in in silico models. In accord with their structure-activity relationship in the primary screen, the best "hits" stabilize HIF1 alpha, upregulate known HIF target genes in a human neuronal line, and exert neuroprotective effects in established model of oxidative stress in cortical neurons.