In eukaryotes, membrane contact sites ( MCS ) allow direct communication between organelles. Plants have evolved a unique type of MCS , inside intercellular pores, the plasmodesmata, where endoplasmic reticulum ( ER )–plasma membrane ( PM ) contacts coincide with regulation of cell‐to‐cell signalling. The molecular mechanism and function of membrane tethering within plasmodesmata remain unknown. Here, we show that the multiple C2 domains and transmembrane region protein ( MCTP ) family, key regulators of cell‐to‐cell signalling in plants, act as ER ‐ PM tethers specifically at plasmodesmata. We report that MCTP s are plasmodesmata proteins that insert into the ER via their transmembrane region while their C2 domains dock to the PM through interaction with anionic phospholipids. A Atmctp3/Atmctp4 loss of function mutant induces plant developmental defects, impaired plasmodesmata function and composition, while MCTP 4 expression in a yeast Δtether mutant partially restores ER ‐ PM tethering. Our data suggest that MCTP s are unique membrane tethers controlling both ER ‐ PM contacts and cell‐to‐cell signalling.
Efficient starch storage in young xylem parenchyma cells is supported by symplasmic phloem unloading and post-phloem transport via parenchymatic vascular rays in the tuberous roots of cassava.
SUMMARYIn plants, intercellular communication and exchange are highly dependent on cell wall bridging structures between adhering cells, so-called plasmodesmata (PD). In our previous genetic screen for PD-deficient Arabidopsis mutants, we described choline transporter-like 1 (CHER1) being important for PD genesis and maturation. Leaves of cher1 mutant plants have up to 10 times less PD, which do not develop to complex structures. Here we utilize the T-DNA insertion mutant cher1-4 and report a deep comparative proteomic workflow for the identification of cell-wall-embedded PD-associated proteins. Analyzing triplicates of cell-wall-enriched fractions in depth by fractionation and quantitative high-resolution mass spectrometry, we compared > 5000 proteins obtained from fully developed leaves. Comparative data analysis and subsequent filtering generated a list of 61 proteins being significantly more abundant in Col-0. This list was enriched for previously described PD-associated proteins. To validate PD association of so far uncharacterized proteins, subcellular localization analyses were carried out by confocal laser-scanning microscopy. This study confirmed the association of PD for three out of four selected candidates, indicating that the comparative approach indeed allowed identification of so far undescribed PD-associated proteins. Performing comparative cell wall proteomics of Nicotiana benthamiana tissue, we observed an increase in abundance of these three selected candidates during sink to source transition. Taken together, our comparative proteomic approach revealed a valuable data set of potential PD-associated proteins, which can be used as a resource to unravel the molecular composition of complex PD and to investigate their function in cell-to-cell communication.
Dendritic cells (DCs) are crucial for the induction of potent antiviral immune responses. In contrast to immature DCs (iDCs), mature DCs (mDCs) are not permissive for infection with herpes simplex virus type 1 (HSV-1). Here, we demonstrate that HSV-1 infection of iDCs and mDCs induces autophagy, which promotes the degradation of lamin A/C, B1, and B2 in iDCs only. This in turn facilitates the nuclear egress of progeny viral capsids and thus the formation of new infectious particles. In contrast, lamin protein levels remain stable in HSV-1–infected mDCs due to an inefficient autophagic flux. Elevated protein levels of KIF1B and KIF2A in mDCs inhibited lamin degradation, likely by hampering autophagosome–lysosome fusion. Therefore, in mDCs, fewer progeny capsids were released from the nuclei into the cytosol, and fewer infectious virions were assembled. We hypothesize that inhibition of autophagic lamin degradation in mDCs represents a very powerful cellular counterstrike to inhibit the production of progeny virus and thus viral spread.
In eukaryotes, membrane contact sites (MCS) allow direct communication between organelles. Plants have evolved unique MCS, the plasmodesmata intercellular pores, which combine endoplasmic reticulum (ER) - plasma membrane (PM) contacts with regulation of cell-to-cell signalling. The molecular mechanism and function of membrane tethering within plasmodesmata remains unknown.Here we show that the Multiple C2 domains and Transmembrane region Protein (MCTP) family, key regulators of cell-to-cell signalling in plants, act as ER - PM tethers specifically at plasmodesmata. We report that MCTPs are core plasmodesmata proteins that insert into the ER via their transmembrane region whilst their C2 domains dock to the PM through interaction with anionic phospholipids. A mctp3/4 loss-of-function mutant induces plant developmental defects while MCTP4 expression in a yeast Δtether mutant partially restores ER-PM tethering. Our data suggest that MCTPs are unique membrane tethers controlling both ER-PM contacts and cell-cell signalling.
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