Genetic and physical interactions between the organellar mechanosensitive ion channel homologs MSL1, MSL2, and MSL3 reveal a role for inter-organellar communication in plant development

Channels of Evolution: Unveiling Evolutionary Patterns in Diatom Ca2+ Signalling

Diatoms are important primary producers in marine and freshwater environments, but little is known about the signalling mechanisms they use to detect changes in their environment. All eukaryotic organisms use Ca2+ signalling to perceive and respond to environmental stimuli, employing a range of Ca2+-permeable ion channels to facilitate the movement of Ca2+ across cellular membranes. We investigated the distribution of different families of Ca2+ channels in diatom genomes, with comparison to other members of the stramenopile lineage. The four-domain voltage-gated Ca2+ channels (Cav) are present in some centric diatoms but almost completely absent in pennate diatoms, whereas single-domain voltage-gated EukCatA channels were found in all diatoms. Glutamate receptors (GLRs) and pentameric ligand-gated ion channels (pLGICs) also appear to have been lost in several pennate species. Transient receptor potential (TRP) channels are present in all diatoms, but have not undergone the significant expansion seen in brown algae. All diatom species analysed lacked the mitochondrial uniporter (MCU), a highly conserved channel type found in many eukaryotes, including several stramenopile lineages. These results highlight the unique Ca2+-signalling toolkit of diatoms and indicate that evolutionary gains or losses of different Ca2+ channels may contribute to differences in cellular-signalling mechanisms between species.

Deciphering the role of mechanosensitive channels in plant root biology: perception, signaling, and adaptive responses

MAIN CONCLUSION

Mechanosensitive channels are integral membrane proteins that rapidly translate extrinsic or intrinsic mechanical tensions into biological responses. They can serve as potential candidates for developing smart-resilient crops with efficient root systems. Mechanosensitive (MS) calcium channels are molecular switches for mechanoperception and signal transduction in all living organisms. Although tremendous progress has been made in understanding mechanoperception and signal transduction in bacteria and animals, this remains largely unknown in plants. However, identification and validation of MS channels such as Mid1-complementing activity channels (MCAs), mechanosensitive-like channels (MSLs), and Piezo channels (PIEZO) has been the most significant discovery in plant mechanobiology, providing novel insights into plant mechanoperception. This review summarizes recent advances in root mechanobiology, focusing on MS channels and their related signaling players, such as calcium ions (Ca2+), reactive oxygen species (ROS), and phytohormones. Despite significant advances in understanding the role of Ca2+ signaling in root biology, little is known about the involvement of MS channel-driven Ca2+ and ROS signaling. Additionally, the hotspots connecting the upstream and downstream signaling of MS channels remain unclear. In light of this, we discuss the present knowledge of MS channels in root biology and their role in root developmental and adaptive traits. We also provide a model highlighting upstream (cell wall sensors) and downstream signaling players, viz., Ca2+, ROS, and hormones, connected with MS channels. Furthermore, we highlighted the importance of emerging signaling molecules, such as nitric oxide (NO), hydrogen sulfide (H2S), and neurotransmitters (NTs), and their association with root mechanoperception. Finally, we conclude with future directions and knowledge gaps that warrant further research to decipher the complexity of root mechanosensing.

Mechanosensing, from forces to structures

Sessile plants evolve diverse structures in response to complex environmental cues. These factors, in essence, involve mechanical stimuli, which must be sensed and coordinated properly by the plants to ensure effective growth and development. While we have accumulated substantial knowledge on plant mechanobiology, how plants translate mechanical information into three-dimensional structures is still an open question. In this review, we summarize our current understanding of plant mechanosensing at different levels, particularly using Arabidopsis as a model plant system. We also attempt to abstract the mechanosensing process and link the gaps from mechanical cues to the generation of complex plant structures. Here we review the recent advancements on mechanical response and transduction in plant morphogenesis, and we also raise several questions that interest us in different sections.

Root osmotic sensing from local perception to systemic responses

Plants face a constantly changing environment, requiring fine tuning of their growth and development. Plants have therefore developed numerous mechanisms to cope with environmental stress conditions. One striking example is root response to water deficit. Upon drought (which causes osmotic stress to cells), plants can among other responses alter locally their root system architecture (hydropatterning) or orientate their root growth to optimize water uptake (hydrotropism). They can also modify their hydraulic properties, metabolism and development coordinately at the whole root and plant levels. Upstream of these developmental and physiological changes, plant roots must perceive and transduce signals for water availability. Here, we review current knowledge on plant osmotic perception and discuss how long distance signaling can play a role in signal integration, leading to the great phenotypic plasticity of roots and plant development.

Mechanotransduction in the spotlight of mechano-sensitive channels

The study of mechanosensitive channels (MS) in living organisms has progressed considerably over the past two decades. The understanding of their roles in mechanosensation and mechanotransduction was consecrated by the awarding of the Nobel Prize in 2021 to A. Patapoutian for his discoveries on the role of MS channels in mechanoperception in humans. In this review, we first summarize the fundamental properties of MS channels and their mode of operation. Then in a second step, we provide an update on the knowledge on the families of MS channels identified in plants and the roles and functions that have been attributed to them.

The Mechanosensitive Ion Channel MSL10 Modulates Susceptibility to Pseudomonas syringae in Arabidopsis thaliana

Plants sense and respond to molecular signals associated with the presence of pathogens and their virulence factors. Mechanical signals generated during pathogenic invasion may also be important, but their contributions have rarely been studied. Here, we investigate the potential role of a mechanosensitive ion channel, MscS-like (MSL)10, in defense against the bacterial pathogen Pseudomonas syringae in Arabidopsis thaliana. We previously showed that overexpression of MSL10-GFP, phospho-mimetic versions of MSL10, and the gain-of-function allele msl10-3G all produce dwarfing, spontaneous cell death, and the hyperaccumulation of reactive oxygen species. These phenotypes are shared by many autoimmune mutants and are frequently suppressed by growth at high temperature in those lines. We found that the same was true for all three MSL10 hypermorphs. In addition, we show that the SGT1/RAR1/HSP90 cochaperone complex was required for dwarfing and ectopic cell death, PAD4 and SID2 were partially required, and the immune regulators EDS1 and NDR1 were dispensable. All MSL10 hypermorphs exhibited reduced susceptibility to infection by P. syringae strain Pto DC3000 and Pto DC3000 expressing the avirulence genes avrRpt2 or avrRpm1 but not Pto DC3000 hrpL and showed an accelerated induction of PR1 expression compared with wild-type plants. Null msl10-1 mutants were delayed in PR1 induction and displayed modest susceptibility to infection by coronatine-deficient P. syringae pv. tomato. Finally, stomatal closure was reduced in msl10-1 loss-of-function mutants in response to P. syringae pv. tomato COR^-. These data show that MSL10 modulates pathogen responses and begin to address the possibility that mechanical signals are exploited by the plant for pathogen perception.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Plant hormone regulation of abiotic stress responses

Plant hormones are signalling compounds that regulate crucial aspects of growth, development and environmental stress responses. Abiotic stresses, such as drought, salinity, heat, cold and flooding, have profound effects on plant growth and survival. Adaptation and tolerance to such stresses require sophisticated sensing, signalling and stress response mechanisms. In this Review, we discuss recent advances in understanding how diverse plant hormones control abiotic stress responses in plants and highlight points of hormonal crosstalk during abiotic stress signalling. Control mechanisms and stress responses mediated by plant hormones including abscisic acid, auxin, brassinosteroids, cytokinins, ethylene and gibberellins are discussed. We discuss new insights into osmotic stress sensing and signalling mechanisms, hormonal control of gene regulation and plant development during stress, hormone-regulated submergence tolerance and stomatal movements. We further explore how innovative imaging approaches are providing insights into single-cell and tissue hormone dynamics. Understanding stress tolerance mechanisms opens new opportunities for agricultural applications.

Recent Advances in the Physiology of Ion Channels in Plants

Our knowledge of plant ion channels was significantly enhanced by the first application of the patch-clamp technique to isolated guard cell protoplasts over 35 years ago. Since then, research has demonstrated the importance of ion channels in the control of gas exchange in guard cells, their role in nutrient uptake in roots, and the participation of calcium-permeable cation channels in the regulation of cell signaling affected by the intracellular concentrations of this second messenger. In recent years, through the employment of reverse genetics, mutant proteins, and heterologous expression systems, research on ion channels has identified mechanisms that modify their activity through protein-protein interactions or that result in activation and/or deactivation of ion channels through posttranslational modifications. Additional and confirmatory information on ion channel functioning has been derived from the crystallization and molecular modeling of plant proteins that, together with functional analyses, have helped to increase our knowledge of the functioning of these important membrane proteins that may eventually help to improve crop yield. Here, an update on the advances obtained in plant ion channel function during the last few years is presented.

Gravity sensing in plant and animal cells

Gravity determines shape of body tissue and affects the functions of life, both in plants and animals. The cellular response to gravity is an active process of mechanotransduction. Although plants and animals share some common mechanisms of gravity sensing in spite of their distant phylogenetic origin, each species has its own mechanism to sense and respond to gravity. In this review, we discuss current understanding regarding the mechanisms of cellular gravity sensing in plants and animals. Understanding gravisensing also contributes to life on Earth, e.g., understanding osteoporosis and muscle atrophy. Furthermore, in the current age of Mars exploration, understanding cellular responses to gravity will form the foundation of living in space.

Corynebacterium glutamicum Mechanosensing: From Osmoregulation to L-Glutamate Secretion for the Avian Microbiota-Gut-Brain Axis

After the discovery of Corynebacterium glutamicum from avian feces-contaminated soil, its enigmatic L-glutamate secretion by corynebacterial MscCG-type mechanosensitive channels has been utilized for industrial monosodium glutamate production. Bacterial mechanosensitive channels are activated directly by increased membrane tension upon hypoosmotic downshock; thus; the physiological significance of the corynebacterial L-glutamate secretion has been considered as adjusting turgor pressure by releasing cytoplasmic solutes. In this review, we present information that corynebacterial mechanosensitive channels have been evolutionally specialized as carriers to secrete L-glutamate into the surrounding environment in their habitats rather than osmotic safety valves. The lipid modulation activation of MscCG channels in L-glutamate production can be explained by the "Force-From-Lipids" and "Force-From-Tethers" mechanosensing paradigms and differs significantly from mechanical activation upon hypoosmotic shock. The review also provides information on the search for evidence that C. glutamicum was originally a gut bacterium in the avian host with the aim of understanding the physiological roles of corynebacterial mechanosensing. C. glutamicum is able to secrete L-glutamate by mechanosensitive channels in the gut microbiota and help the host brain function via the microbiota-gut-brain axis.

Discoveries in structure and physiology of mechanically activated ion channels

The ability to sense physical forces is conserved across all organisms. Cells convert mechanical stimuli into electrical or chemical signals via mechanically activated ion channels. In recent years, the identification of new families of mechanosensitive ion channels-such as PIEZO and OSCA/TMEM63 channels-along with surprising insights into well-studied mechanosensitive channels have driven further developments in the mechanotransduction field. Several well-characterized mechanosensory roles such as touch, blood-pressure sensing and hearing are now linked with primary mechanotransducers. Unanticipated roles of mechanical force sensing continue to be uncovered. Furthermore, high-resolution structures representative of nearly every family of mechanically activated channel described so far have underscored their diversity while advancing our understanding of the biophysical mechanisms of pressure sensing. Here we summarize recent discoveries in the physiology and structures of known mechanically activated ion channel families and discuss their implications for understanding the mechanisms of mechanical force sensing.

Interactions between the N- and C-termini of the mechanosensitive ion channel AtMSL10 are consistent with a three-step mechanism for activation

Although a growing number of mechanosensitive ion channels are being identified in plant systems, the molecular mechanisms by which they function are still under investigation. Overexpression of the mechanosensitive ion channel MSL (MscS-Like)10 fused to green fluorescent protein (GFP) triggers a number of developmental and cellular phenotypes including the induction of cell death, and this function is influenced by seven phosphorylation sites in its soluble N-terminus. Here, we show that these and other phenotypes required neither overexpression nor a tag, and could also be induced by a previously identified point mutation in the soluble C-terminus (S640L). The promotion of cell death and hyperaccumulation of H2O2 in 35S:MSL10S640L-GFP overexpression lines was suppressed by N-terminal phosphomimetic substitutions, and the soluble N- and C-terminal domains of MSL10 physically interacted. We propose a three-step model by which tension-induced conformational changes in the C-terminus could be transmitted to the N-terminus, leading to its dephosphorylation and the induction of adaptive responses. Taken together, this work expands our understanding of the molecular mechanisms of mechanotransduction in plants.