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Plant Physiology Aug 2023For multicellular organisms to develop, cells must grow, divide, and differentiate along preferential or exclusive orientations or directions. Moreover, those...
For multicellular organisms to develop, cells must grow, divide, and differentiate along preferential or exclusive orientations or directions. Moreover, those orientations, or axes, and directions, or polarities, must be coordinated between cells within and between tissues. Therefore, how axes and polarities are coordinated between cells is a key question in biology. In animals, such coordination mainly depends on cell migration and direct interaction between proteins protruding from the plasma membrane. Both cell movements and direct cell-cell interactions are prevented in plants by cell walls that surround plant cells and keep them apart and in place. Therefore, plants have evolved unique mechanisms to coordinate their cell axes and polarities. Here I will discuss evidence suggesting that understanding how leaf veins form may uncover those unique mechanisms. Indeed, unlike previously thought, the cell-to-cell polar transport of the plant hormone auxin along developing veins cannot account for many features of vein patterning. Instead, those features can be accounted for by models of vein patterning that combine polar auxin transport with auxin diffusion through plasmodesmata along the axis of developing veins. Though it remains unclear whether such a combination of polar transport and axial diffusion of auxin can account for the formation of the variety of vein patterns found in plant leaves, evidence suggests that such a combined mechanism may control plant developmental processes beyond vein patterning.
Topics: Plant Growth Regulators; Indoleacetic Acids; Biological Transport; Plants; Plant Leaves
PubMed: 37261944
DOI: 10.1093/plphys/kiad321 -
The Plant Journal : For Cell and... Jul 2023In the present study, we present callus grafting, comprising a method for reproducibly generating tissue chimeras from callus cultures of Arabidopsis thaliana. In this...
In the present study, we present callus grafting, comprising a method for reproducibly generating tissue chimeras from callus cultures of Arabidopsis thaliana. In this way, callus cultures of different genetic backgrounds may be co-cultivated such that cell-to-cell connectivity is achieved as a chimeric tissue is formed. To track intercellular connectivity and transport between non-clonal callus cells, we used transgenic lines expressing fluorescently tagged mobile and non-mobile fusion constructs. Using fluorescently-labelled reporter lines that label plasmodesmata, we show that secondary complex plasmodesmata are present at the cell walls of connected cells. We use this system to investigate cell-to-cell transport across the callus graft junction and show that different proteins and RNAs are mobile between non-clonal callus cells. Finally, we take advantage of the callus culture system to probe intercellular connectivity of grafted leaf and root calli and the effect of different light regimes of cell-to-cell transport. Taking advantage of the ability of callus to be cultivated in the complete absence of light, we show that the rate of silencing spread is significantly decreased in chimeric calli cultivated in total darkness. We propose that callus grafting is a fast and reliable method for analysing the capacity of a macromolecule to be exchanged between cells independent of the vasculature.
Topics: Arabidopsis; Biological Transport; Arabidopsis Proteins; Gene Silencing; Plasmodesmata
PubMed: 37243907
DOI: 10.1111/tpj.16326 -
The Plant Journal : For Cell and... Sep 2023In RNA interference (RNAi), small interfering RNAs (siRNAs) produced from double-stranded RNA guide ARGONAUTE (AGO) proteins to silence sequence-complementary RNA/DNA....
In RNA interference (RNAi), small interfering RNAs (siRNAs) produced from double-stranded RNA guide ARGONAUTE (AGO) proteins to silence sequence-complementary RNA/DNA. RNAi can propagate locally and systemically in plants, but despite recent advances in our understanding of the underlying mechanisms, basic questions remain unaddressed. For instance, RNAi is inferred to diffuse through plasmodesmata (PDs), yet how its dynamics in planta compares with that of established symplastic diffusion markers remains unknown. Also is why select siRNA species, or size classes thereof, are apparently recovered in RNAi recipient tissues, yet only under some experimental settings. Shootward movement of endogenous RNAi in micro-grafted Arabidopsis is also yet to be achieved, while potential endogenous functions of mobile RNAi remain scarcely documented. Here, we show (i) that temporal, localized PD occlusion in source leaves' companion cells (CCs) suffices to abrogate all systemic manifestations of CC-activated mobile transgene silencing, including in sink leaves; (ii) that the presence or absence of specific AGOs in incipient/traversed/recipient tissues likely explains the apparent siRNA length selectivity observed upon vascular movement; (iii) that stress enhancement allows endo-siRNAs of a single inverted repeat (IR) locus to translocate against the shoot-to-root phloem flow; and (iv) that mobile endo-siRNAs generated from this locus have the potential to regulate hundreds of transcripts. Our results close important knowledge gaps, rationalize previously noted inconsistencies between mobile RNAi settings, and provide a framework for mobile endo-siRNA research.
Topics: RNA, Small Interfering; RNA, Double-Stranded; Arabidopsis; RNA Interference; Argonaute Proteins; Bias
PubMed: 37243897
DOI: 10.1111/tpj.16327 -
The Plant Cell Aug 2023Effective cellular signaling relies on precise spatial localization and dynamic interactions among proteins in specific subcellular compartments or niches, such as...
Effective cellular signaling relies on precise spatial localization and dynamic interactions among proteins in specific subcellular compartments or niches, such as cell-to-cell contact sites and junctions. In plants, endogenous and pathogenic proteins gained the ability to target plasmodesmata, membrane-lined cytoplasmic connections, through evolution to regulate or exploit cellular signaling across cell wall boundaries. For example, the receptor-like membrane protein PLASMODESMATA-LOCATED PROTEIN 5 (PDLP5), a potent regulator of plasmodesmal permeability, generates feed-forward or feed-back signals important for plant immunity and root development. However, the molecular features that determine the plasmodesmal association of PDLP5 or other proteins remain largely unknown, and no protein motifs have been identified as plasmodesmal targeting signals. Here, we developed an approach combining custom-built machine-learning algorithms and targeted mutagenesis to examine PDLP5 in Arabidopsis thaliana and Nicotiana benthamiana. We report that PDLP5 and its closely related proteins carry unconventional targeting signals consisting of short stretches of amino acids. PDLP5 contains 2 divergent, tandemly arranged signals, either of which is sufficient for localization and biological function in regulating viral movement through plasmodesmata. Notably, plasmodesmal targeting signals exhibit little sequence conservation but are located similarly proximal to the membrane. These features appear to be a common theme in plasmodesmal targeting.
Topics: Arabidopsis Proteins; Plasmodesmata; Arabidopsis; Membrane Proteins; Carrier Proteins
PubMed: 37225403
DOI: 10.1093/plcell/koad152 -
Journal of Experimental Botany Aug 2023Plasmodesmata (PD) are plasma membrane-lined cytoplasmic nanochannels that mediate cell-to-cell communication across the cell wall. A range of proteins are embedded in...
Plasmodesmata (PD) are plasma membrane-lined cytoplasmic nanochannels that mediate cell-to-cell communication across the cell wall. A range of proteins are embedded in the PD plasma membrane and endoplasmic reticulum (ER), and function in regulating PD-mediated symplasmic trafficking. However, knowledge of the nature and function of the ER-embedded proteins in the intercellular movement of non-cell-autonomous proteins is limited. Here, we report the functional characterization of two ER luminal proteins, AtBiP1/2, and two ER integral membrane proteins, AtERdj2A/B, which are located within the PD. These PD proteins were identified as interacting proteins with cucumber mosaic virus (CMV) movement protein (MP) in co-immunoprecipitation studies using an Arabidopsis-derived plasmodesmal-enriched cell wall protein preparation (PECP). The AtBiP1/2 PD location was confirmed by TEM-based immunolocalization, and their AtBiP1/2 signal peptides (SPs) function in PD targeting. In vitro/in vivo pull-down assays revealed the association between AtBiP1/2 and CMV MP, mediated by AtERdj2A, through the formation of an AtBiP1/2-AtERdj2-CMV MP complex within PD. The role of this complex in CMV infection was established, as systemic infection was retarded in bip1/bip2w and erdj2b mutants. Our findings provide a model for a mechanism by which the CMV MP mediates cell-to-cell trafficking of its viral ribonucleoprotein complex.
Topics: Arabidopsis; Plasmodesmata; Cucumovirus; Endoplasmic Reticulum; Cytomegalovirus Infections; Plant Viral Movement Proteins; Nicotiana
PubMed: 37210666
DOI: 10.1093/jxb/erad190 -
The New Phytologist Jul 2023Volume and surface area of chloroplasts and surface area of plasmodesmata pit fields are presented for two C species, maize and sugarcane, with respect to cell surface...
Volume and surface area of chloroplasts and surface area of plasmodesmata pit fields are presented for two C species, maize and sugarcane, with respect to cell surface area and cell volume. Serial block face scanning electron microscopy (SBF-SEM) and confocal laser scanning microscopy with the Airyscan system (LSM) were used. Chloroplast size estimates were much faster and easier using LSM than with SBF-SEM; however, the results were more variable than SBF-SEM. Mesophyll cells were lobed where chloroplasts were located, facilitating cell-to-cell connections while allowing for greater intercellular airspace exposure. Bundle sheath cells were cylindrical with chloroplasts arranged centrifugally. Chloroplasts occupied c. 30-50% of mesophyll cell volume, and 60-70% of bundle sheath cell volume. Roughly 2-3% of each cell surface area was covered by plasmodesmata pit fields for both bundle sheath and mesophyll cells. This work will aid future research to develop SBF-SEM methodologies with the aim to better understand the effect of cell structure on C photosynthesis.
Topics: Zea mays; Saccharum; Plasmodesmata; Chloroplasts; Plant Leaves; Photosynthesis; Mesophyll Cells; Edible Grain
PubMed: 37194956
DOI: 10.1111/nph.18956 -
International Journal of Molecular... Apr 2023This review focuses on the regulation of root water uptake in plants which are exposed to salt stress. Root water uptake is not considered in isolation but is viewed in... (Review)
Review
This review focuses on the regulation of root water uptake in plants which are exposed to salt stress. Root water uptake is not considered in isolation but is viewed in the context of other potential tolerance mechanisms of plants-tolerance mechanisms which relate to water relations and gas exchange. Plants spend between one third and half of their lives in the dark, and salt stress does not stop with sunset, nor does it start with sunrise. Surprisingly, how plants deal with salt stress during the dark has received hardly any attention, yet any growth response to salt stress over days, weeks, months and years is the integrative result of how plants perform during numerous, consecutive day/night cycles. As we will show, dealing with salt stress during the night is a prerequisite to coping with salt stress during the day. We hope to highlight with this review not so much what we know, but what we do not know; and this relates often to some rather basic questions.
Topics: Plant Leaves; Water; Salt Stress; Plants; Plant Roots
PubMed: 37175779
DOI: 10.3390/ijms24098070 -
International Journal of Molecular... Apr 2023Grafting is widely used to improve the stress tolerance and the fruit yield of horticultural crops. Ribonucleoprotein complexes formed by mRNAs and proteins play...
Grafting is widely used to improve the stress tolerance and the fruit yield of horticultural crops. Ribonucleoprotein complexes formed by mRNAs and proteins play critical roles in the communication between scions and stocks of grafted plants. In Pyrus betulaefolia, ankyrin was identified previously to promote the long-distance movement of the ribonucleoprotein complex(PbPTB3) by facilitating callose degradation at plasmodesmata. However, the mechanism of the ankyrin-mediated callose degradation remains elusive. In this study, we discovered a β-1,3-glucanase (EC 3.2.1.39, PbPDBG) using ankyrin as a bait from plasmodesmata by co-immunoprecipitation and mass spectrometry. Ankyrin was required for the plasmodesmata-localization of PbPDBG. The grafting and bombardment experiments indicated that overexpressing PbPDBG resulted in decreased callose content at plasmodesmata, and thereby promoting the long-distance transport of the ribonucleoprotein complex. Altogether, our findings revealed that PbPDBG was the key factor in ankyrin-mediated callose degradation at plasmodesmata.
Topics: Plasmodesmata; Pyrus; Ankyrins; Crops, Agricultural; Ribonucleoproteins
PubMed: 37175758
DOI: 10.3390/ijms24098051 -
Molecular Plant Pathology Aug 2023The tomato Tm-2 gene was considered to be one of the most durable resistance genes in agriculture, protecting against viruses of the Tobamovirus genus, such as tomato...
The tomato Tm-2 gene was considered to be one of the most durable resistance genes in agriculture, protecting against viruses of the Tobamovirus genus, such as tomato mosaic virus (ToMV) and tobacco mosaic virus (TMV). However, an emerging tobamovirus, tomato brown rugose fruit virus (ToBRFV), has overcome Tm-2 , damaging tomato production worldwide. Tm-2 encodes a nucleotide-binding leucine-rich repeat (NLR) class immune receptor that recognizes its effector, the tobamovirus movement protein (MP). Previously, we found that ToBRFV MP (MP ) enabled the virus to overcome Tm-2 -mediated resistance. Yet, it was unknown how Tm-2 remained durable against other tobamoviruses, such as TMV and ToMV, for over 60 years. Here, we show that a conserved cysteine (C68) in the MP of TMV (MP ) plays a dual role in Tm-2 activation and viral movement. Substitution of MP amino acid H67 with the corresponding amino acid in MP (C68) activated Tm-2 -mediated resistance. However, replacement of C68 in TMV and ToMV disabled the infectivity of both viruses. Phylogenetic and structural prediction analysis revealed that C68 is conserved among all Solanaceae-infecting tobamoviruses except ToBRFV and localizes to a predicted jelly-roll fold common to various MPs. Cell-to-cell and subcellular movement analysis showed that C68 is required for the movement of TMV by regulating the MP interaction with the endoplasmic reticulum and targeting it to plasmodesmata. The dual role of C68 in viral movement and Tm-2 immune activation could explain how TMV was unable to overcome this resistance for such a long period.
Topics: Tobacco Mosaic Virus; Cysteine; Phylogeny; Tobamovirus; Nicotiana; Plant Viral Movement Proteins
PubMed: 37086003
DOI: 10.1111/mpp.13318 -
Proceedings of the National Academy of... Apr 2023The plant immune system relies on the perception of molecules that signal the presence of a microbe threat. This triggers signal transduction that mediates a range of...
The plant immune system relies on the perception of molecules that signal the presence of a microbe threat. This triggers signal transduction that mediates a range of cellular responses via a collection of molecular machinery including receptors, small molecules, and enzymes. One response to pathogen perception is the restriction of cell-to-cell communication by plasmodesmal closure. We previously found that while chitin and flg22 trigger specialized immune signaling cascades in the plasmodesmal plasma membrane, both execute plasmodesmal closure via callose synthesis at the plasmodesmata. Therefore, the signaling pathways ultimately converge at or upstream of callose synthesis. To establish the hierarchy of signaling at plasmodesmata and characterize points of convergence in microbe elicitor-triggered signaling, we profiled the dependence of plasmodesmal responses triggered by different elicitors on a range of plasmodesmal signaling machinery. We identified that, like chitin, flg22 signals via RESPIRATORY BURST OXIDASE HOMOLOGUE D (RBOHD) to induce plasmodesmal closure. Further, we found that PLASMODESMATA-LOCATED PROTEIN 1 (PDLP1), PDLP5, and CALLOSE SYNTHASE 1 (CALS1) are common to microbe- and salicylic acid (SA)-triggered responses, identifying PDLPs as a candidate signaling nexus. To understand how PDLPs relay a signal to CALS1, we screened for PDLP5 interactors and found NON-RACE SPECIFIC DISEASE RESISTANCE/HIN1 HAIRPIN-INDUCED-LIKE protein 3 (NHL3), which is also required for chitin-, flg22- and SA-triggered plasmodesmal responses and PDLP-mediated activation of callose synthesis. We conclude that a PDLP-NHL3 complex acts as an integrating node of plasmodesmal signaling cascades, transmitting multiple immune signals to activate CALS1 and plasmodesmata closure.
Topics: Arabidopsis Proteins; Arabidopsis; Plasmodesmata; Signal Transduction; Salicylic Acid; Chitin
PubMed: 37068237
DOI: 10.1073/pnas.2216397120