Cytokinins Stimulate Plasmodesmatal Transport in Leaves

Glucosinolates can act as signals to modulate intercellular trafficking via plasmodesmata

Plasmodesmata (PD) allow direct communication across the cellulosic plant cell wall, facilitating the intercellular movement of metabolites and signaling molecules within the symplast. In Arabidopsis thaliana embryos with reduced levels of the chloroplast RNA helicase ISE2, intercellular trafficking and the number of branched PD were increased. We therefore investigated the relationship between altered ISE2 expression and intercellular trafficking. Gene expression analyses in Arabidopsis tissues where ISE2 expression was increased or decreased identified genes associated with the metabolism of glucosinolates (GLSs) as highly affected. Concomitant with changes in the expression of GLS-related genes, plants with abnormal ISE2 expression contained altered GLS metabolic profiles compared with wild-type (WT) counterparts. Indeed, changes in the expression of GLS-associated genes led to altered intercellular trafficking in Arabidopsis leaves. Exogenous application of GLSs but not their breakdown products also resulted in altered intercellular trafficking. These changes in trafficking may be mediated by callose levels at PD as exogenous GLS treatment was sufficient to modulate plasmodesmal callose in WT plants. Furthermore, auxin metabolism was perturbed in plants with increased indole-type GLS levels. These findings suggest that GLSs, which are themselves transported between cells via PD, can act on PD to regulate plasmodesmal trafficking capacity.

Emerging into the world: regulation and control of dormancy and sprouting in geophytes

Geophytic plants synchronize growth and quiescence with the external environment to survive and thrive under changing seasons. Together with seasonal growth adaptation, dormancy and sprouting are critical factors determining crop yield and market supply, as various geophytes also serve as major food, floriculture, and ornamental crops. Dormancy in such crops determines crop availability in the market, as most of them are consumed during the dormant stage. On the other hand, uniform/maximal sprouting is crucial for maximum yield. Thus, dormancy and sprouting regulation have great economic importance. Dormancy-sprouting cycles in geophytes are regulated by genetic, exogenous (environmental), and endogenous (genetic, metabolic, hormonal, etc.) factors. Comparatively, the temperature is more dominant in regulating dormancy and sprouting in geophytes, unlike above-ground tissues, where both photoperiod and temperature control are involved. Despite huge economic importance, studies concerning the regulation of dormancy and sprouting are scarce in the majority of geophytes. To date, only a few molecular factors involved in the process have been suggested. Recently, omics studies on molecular and metabolic factors involved in dormancy and growth regulation of underground vegetative tissues have provided more insight into the mechanism. Here, we discuss current knowledge of the environmental and molecular regulation and control of dormancy and sprouting in geophytes, and discuss challenges/questions that need to be addressed in the future for crop improvement.

Plasmodesmata: Channels Under Pressure

Multicellularity has emerged multiple times in evolution, enabling groups of cells to share a living space and reducing the burden of solitary tasks. While unicellular organisms exhibit individuality and independence, cooperation among cells in multicellular organisms brings specialization and flexibility. However, multicellularity also necessitates intercellular dependence and relies on intercellular communication. In plants, this communication is facilitated by plasmodesmata: intercellular bridges that allow the direct (cytoplasm-to-cytoplasm) transfer of information between cells. Plasmodesmata transport essential molecules that regulate plant growth, development, and stress responses. They are embedded in the extracellular matrix but exhibit flexibility, adapting intercellular flux to meet the plant's needs.In this review, we delve into the formation and functionality of plasmodesmata and examine the capacity of the plant communication network to respond to developmental and environmental cues. We illustrate how environmental pressure shapes cellular interactions and aids the plant in adapting its growth.

Communicating Across Cell Walls: Structure, Evolution, and Regulation of Plasmodesmatal Transport in Plants

Plasmodesmata are conduits in plant cell walls that allow neighboring cells to communicate and exchange resources. Despite their central importance to plant development and physiology, our understanding of plasmodesmata is relatively limited compared to other subcellular structures. In recent years, technical advances in electron microscopy, mass spectrometry, and phylogenomics have illuminated the structure, composition, and evolution of plasmodesmata in diverse plant lineages. In parallel, forward genetic screens have revealed key signaling pathways that converge to regulate plasmodesmatal transport, including chloroplast-derived retrograde signaling, phytohormone signaling, and metabolic regulation by the conserved eukaryotic Target of Rapamycin kinase. This review summarizes our current knowledge of the structure, evolution, and regulation of plasmodesmatal transport in plants.

Regulating bulb dormancy release and flowering in lily through chemical modulation of intercellular communication

Lily is a bulbous plant with an endogenous dormancy trait. Fine-tuning bulb dormancy release is still a challenge in the development of bulb storage technology. In this study, we identified three regulators of symplastic transport, 2,3-Butanedione oxime (BDM), N-Ethyl maleimide (NEM), and 2-Deoxy-D-glucose (DDG), that also regulate bulb dormancy release. We demonstrated that BDM and DDG inhibited callose synthesis between cells and promoted symplastic transport and soluble sugars in the shoot apical meristem (SAM), eventually accelerating bulb dormancy release and flowering in lilies. Conversely, NEM had the opposite effect. These three regulators can be flexibly applied to either accelerate or delay lily bulb dormancy release.

Heavy Metal-Associated Isoprenylated Plant Proteins (HIPPs) at Plasmodesmata: Exploring the Link between Localization and Function

Heavy metal-associated isoprenylated plant proteins (HIPPs) are a metallochaperone-like protein family comprising a combination of structural features unique to vascular plants. HIPPs possess both one or two heavy metal-binding domains and an isoprenylation site, facilitating a posttranslational protein lipid modification. Recent work has characterized individual HIPPs across numerous different species and provided evidence for varied functionalities. Interestingly, a significant number of HIPPs have been identified in proteomes of plasmodesmata (PD)-nanochannels mediating symplastic connectivity within plant tissues that play pivotal roles in intercellular communication during plant development as well as responses to biotic and abiotic stress. As characterized functions of many HIPPs are linked to stress responses, plasmodesmal HIPP proteins are potentially interesting candidate components of signaling events at or for the regulation of PD. Here, we review what is known about PD-localized HIPP proteins specifically, and how the structure and function of HIPPs more generally could link to known properties and regulation of PD.

Is auxin enough? Cytokinins and margin patterning in simple leaves

The interplay between auxin and cytokinins affects facets of plant development as different as ovule formation and lateral root initiation. Moreover, cytokinins favor complexity in the development of Solanum lycopersicum and Cardamine hirsuta compound leaves. Nevertheless, no role has been proposed for cytokinins in patterning the margins of the simple leaves of Arabidopsis thaliana, a process that is assumed to be sufficiently explained by auxin localization. Here, we discuss evidence supporting the hypothesis that cytokinins play a role in simple leaf margin morphogenesis via crosstalk with auxin, as occurs in other plant developmental events. Indeed, mutant or transgenic arabidopsis plants defective in cytokinin biosynthesis or signaling, or with increased cytokinin degradation have leaf margins less serrated than the wild type.

Quantifying Plasmodesmatal Transport with an Improved GFP Movement Assay

Plasmodesmata (PD) are membrane-lined channels that cross the cell wall to connect the cytosol of adjacent plant cells, permitting diverse cytosolic molecules to move between cells. PD are essential for plant multicellularity, and the regulation of PD transport contributes to metabolism, developmental patterning, abiotic stress responses, and pathogen defenses, which has sparked broad interest in PD among diverse plant biologists. Here, we present a straightforward method to reproducibly quantify changes in the rate of PD transport in leaves. Individual cells are transformed with Agrobacterium to express fluorescent proteins, which then move beyond the transformed cell via PD. Forty-eight to 72 h later, the extent of GFP movement is monitored by confocal fluorescence microscopy. This assay is versatile and may be combined with transient gene overexpression, virus-induced gene silencing, physiological treatments, or pharmaceutical treatments to test how PD transport responds to specific conditions. We expect that this improved method for monitoring PD transport in leaves will be broadly useful for plant biologists working in diverse fields.