Clathrin-mediated endocytosis-independent function of VAN3 ARF GTPase Activating Protein at the plasma membrane

ARF small GTPases in plants serve important cellular functions in subcellular trafficking and developmental functions in auxin-mediated patterning of the plant body. The Arabidopsis thaliana ARF regulator ARF-GAP VAN3 has been implicated to act at the plasma membrane (PM) and linked functionally to the clathrin- and dynamin-mediated endocytosis. Here we re-evaluated the localization of VAN3 at the PM and its function in endocytosis. Using Total Internal Reflection Fluorescence microscopy we observed remarkably transient associations of VAN3 to the PM at discrete foci, however, devoid of clathrin, the dynamin isoform DRP1A, or the ARF regulator GNOM, which is also involved in a developmental patterning function mediated from the PM. Clathrin-coated pits are abundant and endocytosis appears to proceed normally in van3-1 knockout mutant. In turn, post-translational silencing of clathrin expression indicates that the localization of VAN3 at the PM depends on clathrin function, presumably on clathrin-mediated endocytosis.

Delta-1 variant of SARS-COV-2 acquires spike V1264L and drives the pandemic in Indonesia, Singapore and Malaysia

Since April 2021, delta variant of SARS-COV-2 has gradually overtaken all other variants and become a dominant pandemic driver around the world. It has evolved and yielded four subvariants: delta1, delta2, delta3 and delta4. While trying to understand how these subvariants drive the pandemic in Southeast Asia, I noticed that many d1 genomes from Indonesia encode an extra spike substitution, V1264L. Coincidentally, this confers an acidic dileucine motif because residues 1157-1262 are acidic and residue 1265 is leucine. Such a motif may affect subcellular trafficking of the resulting spike protein. Alarmingly, this V1264L-encoding delta1 subvariant (referred to as delta1L) has become the dominant pandemic driver in Indonesia, Singapore, Malaysia and East Timor. Moreover, it has acquired additional spike substitutions: L1234L in Singapore and D215Y/N in Malaysia. On the average, the resulting sublineages carry 46-48 mutations per genome, making them some of the most mutated variants identified so far. Moreover, a d1 sublineage from the United Kingdom has acquired V1264L along with spike Y145H and A222V, a signature substitution of a SARS-COV-2 clade that was a major pandemic driver in Europe during the summer of 2020. A222V improves an extensive hydrophobic interaction network at the N-terminal domain of spike protein and may make this sublineage more virulent than delta1 and delta1L. Some delta2 subvariant genomes identified in the United States of America and other countries also encode V1264L. Thus, V1264L is a recurrent spike substitution frequently acquired by d subvariants during convergent evolution. This recurrence also suggests that V1264L is one key mechanism by which d variant adopts to expand its ‘evolutionary cage.’

Co-evolutionary analysis suggests a role for TLR9 in papillomavirus restriction

A.AbstractUpon infection, DNA viruses can be sensed by pattern recognition receptors (PRRs) leading to the activation of type I and III interferons, aimed at blocking infection. Therefore, viruses must inhibit these signaling pathways, avoid being detected, or both. Papillomavirus virions are trafficked from early endosomes to the Golgi apparatus and wait for the onset of mitosis to complete nuclear entry. This unique subcellular trafficking strategy avoids detection by cytoplasmic PRRs, a property that may contribute to establishment of infection. However, as the capsid uncoats within acidic endosomal compartments, the viral DNA may be exposed to detection by toll-like receptor (TLR) 9. In this study we characterize two new papillomaviruses from bats and use molecular archeology to demonstrate that their genomes altered their nucleotide composition to avoid detection by TLR9, providing evidence that TLR9 acts as a PRR during papillomavirus infection. Furthermore, we demonstrate that TLR9, like other components of the innate immune system, is under evolutionary selection in bats, providing the first direct evidence for co-evolution between papillomaviruses and their hosts.

Receptor kinase module targets PIN-dependent auxin transport during canalization

Spontaneously arising channels that transport the phytohormone auxin provide positional cues for self-organizing aspects of plant development such as flexible vasculature regeneration or its patterning during leaf venation. The auxin canalization hypothesis proposes a feedback between auxin signaling and transport as the underlying mechanism, but molecular players await discovery. We identified part of the machinery that routes auxin transport. The auxin-regulated receptor CAMEL (Canalization-related Auxin-regulated Malectin-type RLK) together with CANAR (Canalization-related Receptor-like kinase) interact with and phosphorylate PIN auxin transporters. camel and canar mutants are impaired in PIN1 subcellular trafficking and auxin-mediated PIN polarization, which macroscopically manifests as defects in leaf venation and vasculature regeneration after wounding. The CAMEL-CANAR receptor complex is part of the auxin feedback that coordinates polarization of individual cells during auxin canalization.

The manifold actions of signaling peptides on subcellular dynamics of a receptor specify stomatal cell fate

Receptor endocytosis is important for signal activation, transduction, and deactivation. However, how a receptor interprets conflicting signals to adjust cellular output is not clearly understood. Using genetic, cell biological, and pharmacological approaches, we report here that ERECTA-LIKE1 (ERL1), the major receptor restricting plant stomatal differentiation, undergoes dynamic subcellular behaviors in response to different EPIDERMAL PATTERNING FACTOR (EPF) peptides. Activation of ERL1 by EPF1 induces rapid ERL1 internalization via multivesicular bodies/late endosomes to vacuolar degradation, whereas ERL1 constitutively internalizes in the absence of EPF1. The co-receptor, TOO MANY MOUTHS is essential for ERL1 internalization induced by EPF1 but not by EPFL6. The peptide antagonist, Stomagen, triggers retention of ERL1 in the endoplasmic reticulum, likely coupled with reduced endocytosis. In contrast, the dominant-negative ERL1 remained dysfunctional in ligand-induced subcellular trafficking. Our study elucidates that multiple related yet unique peptides specify cell fate by deploying the differential subcellular dynamics of a single receptor.