Callose balancing at plasmodesmata

Abstract

In plants, communication and molecular exchanges between different cells and tissues are dependent on the apoplastic and symplastic pathways. Symplastic molecular exchanges take place through the plasmodesmata, which connect the cytoplasm of neighboring cells in a highly controlled manner. Callose, a β-1,3-glucan polysaccharide, is a plasmodesmal marker molecule that is deposited in cell walls near the neck zone of plasmodesmata and controls their permeability. During cell differentiation and plant development, and in response to diverse stresses, the level of callose in plasmodesmata is highly regulated by two antagonistic enzymes, callose synthase or glucan synthase-like and β-1,3-glucanase. The diverse modes of regulation by callose synthase and β-1,3-glucanase have been uncovered in the past decades through biochemical, molecular, genetic, and omics methods. This review highlights recent findings regarding the function of plasmodesmal callose and the molecular players involved in callose metabolism, and provides new insight into the mechanisms maintaining plasmodesmal callose homeostasis.

Glucosylhydroxyceramides Modulate Secretion Machinery of a Subset of Plasmodesmata Proteins and a Change in the Callose Accumulation

“…S1P in guard triggers alteration in nitric oxide (NO), cytoplasmic calcium and cytoplasmic pH (Ng et al, 2001; Puli et al, 2016). Reactive oxygen species and cytoplasmic calcium are well known trigger of callose accumulation, probably through posttranslational regulation of callose synthases (Xu et al, 2017; Wu et al, 2018). Thus, a reduction of S1P by DMS treatment or in sphk1 mutants may accompany a diminution of callose synthase activity by posttranslational modification.…”

“…Plasmodesmata (PDs), plant-specific symplasmic channels, cross the plant cell wall and physically connect the cytoplasm and endoplasmic reticulum (ER) of contiguous cells. These intercellular channels play important roles in multicellular events during plant development by allowing the molecular exchange of signaling molecules such as transcription factors, RNAs, and growth regulators (Zambryski and Crawford, 2000; Maule, 2008; Wu et al, 2018). The plasmodesmal plasma membrane (PD-PM) is distinct from general cellular plasma membrane (PM) and is characterized by the enrichment of sterols and sphingolipid SL species (Grison et al, 2015; Iswanto and Kim, 2017; Mamode Cassim et al, 2019).…”

CRK2 enhances salt tolerance in Arabidopsis thaliana by regulating endocytosis and callose deposition in connection with PLDα1

“…This is crucial not only for normal plant development and cellular signalling, but also during adverse conditions where the plant may want to either close off communication to isolate an affected cell, or open communication to allow distant cells to respond accordingly. Increased callose deposition has been documented for various stresses (S.-W. Wu et al, 2018), but has not yet been clearly linked to salt stress responses. Here we show that callose deposition is elevated during salt tolerance and the acute response to salt stress, and that NaCl-induced callose deposition is regulated in part by CRK2.…”

Plasmodesmata Conductivity Regulation: A Mechanistic Model

“…A. thaliana AtCalSs are encoded by 12 glucan-synthase-like genes (AtGSL1 to AtGSL12) and are large proteins (1770-1950 amino acids) possessing a large central catalytic domain which includes a UDP-glucose catalytic site and a glycosyltransferase domain surrounded by multiple transmembrane domains [69,118]. CalSs are located in the PM and exhibit high substrate specificity for the nucleotide sugar uridine diphosphate glucose (UDP-glucose) [37,47,119]. Several isoforms of AtCalSs were found in the proteome of trans-Golgi-network-derived vesicles [120] indicating that these proteins are conventionally secreted.…”

“…At the same time, the mechanisms for regulating Pd functions and permeability after stress impacts are still not fully understood. If the negative role of callose in the control of intercellular molecular flow via Pd is convincingly confirmed experimentally [35][36][37], the role of cytoskeletal elements and protein components, called Pd-associated proteins (PdAPs), is mostly unclear [32,38]. The analysis of the Pd proteome revealed that most PdAPs are secreted proteins [39] that might be involved in controlling Pd permeability under abiotic and biotic stress.…”