Biology subjects

Mu, B.

Publications and source records attributed to Mu, B..

3 recordsLinked to original sources

bioRxiv2024

Ca2+-dependent vesicular and non-vesicular lipid transfer controls hypoosmotic plasma membrane expansion

Robust coordination of surface and volume changes is critical for cell integrity. Few studies have elucidated the plasma membrane (PM) remodeling events during cell surface and volume alteration, especially regarding PM sensing and its subsequent rearrangements. Here, using fission yeast protoplasts, we reveal a Ca2+-dependent mechanism for membrane addition that ensures PM integrity and allows its expansion during acute hypoosmotic cell swelling. We show that MscS-like mechanosensitive channels activated by PM tension control extracellular Ca2+ influx, which triggers direct lipid transfer at endoplasmic reticulum (ER)-PM contact sites by conserved extended-synaptotagmins and accelerates exocytosis, enabling PM expansion necessary for osmotic equilibrium. Defects in any of these key events result in rapid protoplast rupture upon severe hypotonic shock. Our numerical simulations of hypoosmotic expansion further propose a cellular strategy that combines instantaneous non-vesicular lipid transfer with bulk exocytic membrane delivery to maintain PM integrity for dramatic cell surface/volume adaptation.

cell biology↗

bioRxiv2023

Knockout of endoplasmic reticulum localized molecular chaperone HSP90.7 impairs seeding development and cellular auxin homeostasis in Arabidopsis

The Arabidopsis endoplasmic reticulum localized heat shock protein HSP90.7 modulates tissue differentiation and stress responses; however, complete knockout lines have not been previously reported. In this study, we identified and analyzed a mutant allele, hsp90.7-1, which did not express any protein and showed seedling lethality. Microscopic analyses revealed its essential role in male and female fertility, trichomes and root hairs development, proper chloroplast function, and in apical meristem maintenance and differentiation. Comparative transcriptome and proteome analyses also revealed a role of the protein in a multitude of cellular processes. Particularly, the auxin responsive pathway was specifically down-regulated in the hsp90.7-1 mutant seedlings. We measured a much-reduced auxin content in both root and shoot tissues. Through comprehensive histological and molecular analyses, we demonstrated PIN1 and PIN5 expressions were dramatically reduced in the mutant, and the TAA-YUCCA primary auxin biosynthesis pathway was also down-regulated, thus revealing a critical new role of HSP90.7 in the regulation of auxin responses. This study therefore not only fulfilled a gap in understanding the essential role of HSP90 paralogs in eukaryotes, but also provided a mechanistic insight on this molecular chaperone in regulating plant growth and development via modulating cellular auxin homeostasis.

plant biology↗

bioRxiv2023

VAP-mediated membrane tethering mechanisms implicate ER-PM contact function in pH homeostasis

VAMP-associated proteins (VAPs) are highly conserved endoplasmic reticulum (ER) resident proteins that establish ER contacts with multiple membrane compartments in many eukaryotes. However, VAP-mediated membrane tethering mechanisms remain ambiguous. Here, focusing on fission yeast ER-plasma membrane (PM) contact formation, using systematic interactome analyses and quantitative microscopy, we predict a non-VAP-protein direct binding-based tethering mechanism of VAPs. We further demonstrate that VAP-anionic phospholipids interactions underlie ER-PM association and define the pH-responsive nature of VAP-tethered membrane contacts. Importantly, such conserved interactions with anionic phospholipids are generally defective in amyotrophic lateral sclerosis (ALS)-associated human VAPB mutant. Moreover, we identify a conserved FFAT-like motif locating at the autoinhibitory hotspot of the essential PM proton pump Pma1. This modulatory VAP-Pma1 interaction is crucial for pH homeostasis. We thus propose an ingenious strategy for maintaining intracellular pH by coupling Pma1 modulation with pH-sensory ER-PM contacts via VAP-mediated interactions.

cell biology↗