Rodrigues, V. | Search bioRxiv

bioRxiv2022

The m6A writer FIONA1 methylates the 3'UTR of FLC and controls flowering in Arabidopsis

Adenosine bases of RNA can be transiently modified by the deposition of a methyl-group to form N6-methyladenosine (m6A). This adenosine-methylation is an ancient process and the enzymes involved are evolutionary highly conserved. A genetic screen designed to identified suppressors of late flowering transgenic Arabidopsis plants overexpressing the miP1a microProtein yielded a new allele of the FIONA1 (FIO1) m6A-methyltransferase. To characterize the early flowering phenotype of fio1 mutant plants we employed an integrative approach of mRNA-seq, Nanopore direct RNA-sequencing and meRIP-seq to identify differentially expressed transcripts as well as differentially methylated mRNAs. We provide evidence that FIO1 is the elusive methylase responsible for the 3-end methylation of the FLOWERING LOCUS C (FLC) transcript. Furthermore, our genetic and biochemical data suggest that 3-methylation stabilizes FLC mRNAs and non-methylated FLC is a target for rapid degradation.

plant biology↗

bioRxiv2022

Release of HIV-1 particles from the viral compartment in macrophages requires an associated cytoskeleton and is driven by mechanical constraints

A defining feature of HIV-1 replication in macrophages is that viral assembly occurs at the limiting membrane of a compartment often named VCC (virus-containing compartments) that is connected to the extracellular medium. The newly formed viral progeny pinches of the membrane and accumulates in the lumen of the VCC. While HIV budding has been extensively studied, very little is known about how viral particles present in the lumen of VCC are released in the extracellular medium. Here we show that the actin dynamics are critical for this process by combining ultrastructural analyses, time-lapse microscopy and perturbations of the actin cytoskeleton. We found that jasplakinolide, which stabilizes actin fibres, inhibited viral release from HIV-1-infected macrophages. Furthermore, in jasplakinolide-treated macrophages, VCC became scattered and no longer co-localized with the integrin CD18, nor the phosphorylated form of the focal adhesion kinase PYK2. Inhibition of PYK2 activity in infected macrophages promoted intracellular retention of viral particles in VCC that were no longer connected to the plasma membrane. Finally, we stimulated the rapid release of viral particles from the VCC by subjecting infected macrophages to frustrated phagocytosis. As macrophages spread on IgG-coated glass surfaces, VCC rapidly migrated to the basal membrane and released their viral content in the extracellular medium, which required their association with CD18 and the actin cytoskeleton. These results highlight that VCC trafficking and virus release are intimately linked to the reorganization of the macrophage actin cytoskeleton in response to external physical cues, suggesting that it might be regulated in tissues by the mechanical stress to which these cells are exposed.

cell biology↗