Endoplasmic Reticulum (ER) Membrane Proteins (LUNAPARKs) are Required for Proper Configuration of the Cortical ER Network in Plant Cells

Abstract

The endoplasmic reticulum (ER) is a large network made of membranous cisternae and tubules, which accounts for a large proportion of the total lipid bilayer endomembrane of the cell. In mammals and yeast, LUNAPARK proteins are preferentially localized at the three-way junctions of the ER network, stabilizing the junctions and establishing the ER architecture. We identified two Arabidopsis homologs and designated them LNPA and LNPB. Subcellular localization analysis with a non-dimerizable type of green fluorescent protein (GFP) revealed that both LNPA and LNPB are predominantly distributed throughout the ER, but not preferentially localized at the three-way junctions. Quantitative analysis of the network in the double mutant lnpa lnpb revealed that deficiency of LNPA and LNPB caused the cortical ER to develop poor ER cisternae and a less dense tubular network. These phenotypes are opposite to those of LNP-deficient mutants of yeast and mammals. Despite the importance of cysteine residues in the zinc finger motif of the yeast LNP homolog (Lnp1p), the corresponding cysteine residues of LNPA were not necessary for the stabilization of ER morphology because replacing the four cysteine residues in the zinc finger motif of the LNPA protein with alanine residues did not affect its function. A significant phenotype of lnpa lnpb is generation of large spherical structures from the ER. Formation of the structures might reduce the amounts of the ER membrane to be used for generating the network, resulting in poor development of the ER network. Taken together, our results suggest that plant LNPs function differently from those in yeast and mammals: they function to distribute ER membranes appropriately throughout the cells.

Pangenomic analysis identifies structural variation associated with heat tolerance in pearl millet

“…From the 591 genes whose expression was previously shown to be associated with SVs (Supplementary Table 13), we identified 25 genes near 27 fdSVs that were present only in the HR group; their expression levels were significantly correlated with the presence of fdSVs (Supplementary Table 17). Notably, one of the fdSVs was positioned close to (360 bp) and upstream of PMA2G02653.1, a gene encoding a protein in the zinc finger family that has a role in the ER system [35][36][37] . This gene was enriched in Gene Ontology (GO) terms associated with the response to temperature Article https://doi.org/10.1038/s41588-023-01302-4 stress (GO: 0050826) and was also responsive to heat stress (Extended Data Fig.…”

Resolving the Cohenian paradox in judicial probability theory

“…GTPase ROOT HAIR DEFECTIVE3 (RHD3) is responsible for the homotypic fusion of the ER membrane (Chen et al, 2011;Stefano et al, 2012;Zhang et al, 2013;Ueda et al, 2016) in a manner similar to the mammalian and yeast homologs atlastins and Sey1p, respectively (McNew et al, 2013); however, the mechanisms underlying the fast and dynamic interconversion of ER tubules and cisternae are yet to be discovered. A redistribution of membrane curvature-inducing proteins, such as the conserved reticulons (Tolley et al, 2008;Sparkes et al, 2009b), and the three-way junction-stabilizing LUNAPARK proteins (Lnps; named for the amino acid sequence LNPARK) (Kriechbaumer et al, 2018;Ueda et al, 2018;Sun et al, 2020a), is likely responsible for the dynamic interconversion of ER forms, but the underlying regulatory mechanisms remain largely unknown.…”

“…A double loss-of-function mutant of the two Arabidopsis Lnps shows an increased abundance of ER sheets with dense fenestration and ER conglomerates (Kriechbaumer et al, 2018;Ueda et al, 2018;Sun et al, 2020a). Combined, the finding that the localized distribution of Lnps in the ER depends on the cellular availability of their interacting protein RHD3, and that Lnps antagonize the role of RHD3 in ER shaping and induce RHD3 degradation via the proteasome pathway (Sun et al, 2020a) mechanistically support the notion that certain ER shapers are dependent on the abundance of other ER shapers for their distribution and function in the ER.…”

A Once-Hidden Endoplasmic Reticulum Matrix Reveals the Totally Tubular Function of LUNAPARKs in Plants

“…It was therefore hypothesized that LNPs raise the ratio of sheets to tubules (Kriechbaumer et al, 2018), a role opposite to that of the animal and yeast homologs. Additionally, because of the presence of large clumps of ER membrane in lnp mutants, it was hypothesized that LNPs play a role in the proper distribution of ER throughout the cell (Ueda et al, 2018).…”