No abstract

The nuclear lamina (NL) is a complex network of nuclear lamins and lamina-associated nuclear membrane proteins, which scaffold the nucleus to maintain structural integrity. In animals, type V intermediate filaments are the main constituents of NL. Plant genomes do not encode any homologs of these intermediate filaments, yet plant nuclei contain lamina-like structures that are present in their nuclei. In Arabidopsis thaliana, CROWDED NUCLEI (CRWN), which are required for maintaining structural integrity of the nucleus and specific perinuclear chromatin anchoring, are strong candidates for plant lamin proteins. Recent studies revealed additional roles of Arabidopsis Nuclear Matrix Constituent Proteins (NMCPs) in modulating plants’ response to pathogen and abiotic stresses. However, detailed analyses of Arabidopsis NMCP activities are challenging due to the presence of multiple homologs and their functional redundancy. In this study, we investigated the sole NMCP gene in the liverwort Marchantia polymorpha (MpNMCP). We found that MpNMCP proteins preferentially were localized to the nuclear periphery. Using CRISPR/Cas9 techniques, we generated an MpNMCP loss-of-function mutant, which displayed reduced growth rate and curly thallus lobes. At an organelle level, MpNMCP mutants did not show any alteration in nuclear morphology. Transcriptome analyses indicated that MpNMCP was involved in regulating biotic and abiotic stress responses. Additionally, a highly repetitive genomic region on the male sex chromosome, which was preferentially tethered at the nuclear periphery in wild-type thalli, decondensed in the MpNMCP mutants and located in the nuclear interior. This perinuclear chromatin anchoring, however, was not directly controlled by MpNMCP. Altogether, our results unveiled that NMCP in plants have conserved functions in modulating stress responses.

Nonsense-mediated decay (NMD) is an RNA surveillance mechanism that detects aberrant transcript features and triggers degradation of erroneous as well as physiological RNAs. Originally considered to be constitutive, NMD is now recognized to be tightly controlled in response to inherent signals and diverse stresses. To gain a better understanding of NMD regulation and its functional implications, we systematically examined feedback control of the central NMD components in two dicot and one monocot species. On the basis of the analysis of transcript features, turnover rates and steady-state levels, up-frameshift (UPF) 1, UPF3 and suppressor of morphological defects on genitalia (SMG) 7, but not UPF2, are under feedback control in both dicots. In the monocot investigated in this study, only SMG7 was slightly induced upon NMD inhibition. The detection of the endogenous NMD factor proteins in Arabidopsis thaliana substantiated a negative correlation between NMD activity and SMG7 amounts. Furthermore, evidence was provided that SMG7 is required for the dephosphorylation of UPF1. Our comprehensive and comparative study of NMD feedback control in plants reveals complex and species-specific attenuation of this RNA surveillance pathway, with critical implications for the numerous functions of NMD in physiology and stress responses.

The capacity for achieving immense specificity and resolution in science increases day to day. Fluorescence-activated nuclear sorting (FANS) offers this great precision, enabling one to count and separate distinct types of nuclei from specific cells of heterogeneous mixtures. We developed a workflow to collect nuclei from Arabidopsis thaliana by FANS according to cell lineage and endopolyploidy level with high efficiency. We sorted GFP-labeled nuclei with different ploidy levels from the epidermal tissue layer of three-day, dark-grown hypocotyls followed by a shift to light for one day and compared them to plants left in the dark. We then accessed early chromatin accessibility patterns associated with skotomorphogenesis and photomorphogenesis by the assay for transposase-accessible chromatin using sequencing (ATAC-seq) within primarily stomatal 2C and fully endoreduplicated 16C nuclei. Our quantitative analysis shows that dark- and light-treated samples in 2C nuclei do not exhibit any different chromatin accessibility landscapes, whereas changes in 16C can be linked to transcriptional changes involved in light response.

The dynamic regulation of the plasma membrane (PM) organization at the nanoscale emerged as a key element shaping the outcome of host-microbe interactions. Protein organization into nanodomains (ND) is often assumed to be linked to the activation of cellular processes. In contrast, we have previously shown that the phosphorylation of the Solanum tuberosum REM1.3 (StREM1.3) N-terminal domain disperses its native ND organization and promotes its inhibitory effect on Potato Virus X (PVX) cell-to-cell movement. Here, we show that the phosphorylation of StREM1.3 modify the chemical environment of numerous residues in its intrinsically-disordered N-terminal domain. We leveraged exploratory screens to identify potential phosphorylation-dependent interactors of StREM1.3. Herewith, we uncovered uncharacterized regulators of PVX cell-to-cell movement, linking StREM1.3 to autophagy, water channels and the actin cytoskeleton. We show that the Solanum tuberosum actin depolymerizing factors 2 (StADF2) alters StREM1.3 NDs and limits PVX cell-to-cell movement in a REMORIN-dependent manner. Mutating a conserved single residue reported to affect ADFs affinity to actin inhibits StADF2 effect on StREM1.3 ND organization and PVX cell-to-cell movement. These observations provide functional links between the organization of plant PM and the actin cytoskeleton and suggests that the alteration of StREM1.3 ND organization promotes plant anti-viral responses. We envision that analogous PM re-organization applies for additional signaling pathways in plants and in other organisms.