A plasmodesmata‐associated β‐1,3‐glucanase in Arabidopsis

Abstract

SummaryPlasmodesmal conductivity is regulated in part by callose turnover, which is hypothesized to be determined by b-1,3-glucan synthase versus glucanase activities. A proteomic analysis of an Arabidopsis thaliana plasmodesmata (Pd)-rich fraction identified a b-1,3-glucanase as present in this fraction. The protein encoded by the putative plasmodesmal associated protein (ppap) gene, termed AtBG_ppap, had previously been found to be a post-translationally modified glycosylphosphatidylinositol (GPI) lipid-anchored protein. When fused to green fluorescent protein (GFP) and expressed in tobacco (Nicotiana tabacum) or Nicotiana benthamiana epidermal cells, this protein displays fluorescence patterns in the endoplasmic reticulum (ER) membrane system, along the cell periphery and in a punctate pattern that co-localizes with aniline blue-stained callose present around the Pd. Plasma membrane localization was verified by co-localization of AtBG_ppap:GFP together with a plasma membrane marker N-[3-triethylammoniumpropyl]-4-[p-diethylaminophenylhexatrienyl] pyridinium dibromide (FM4-64) in plasmolysed cells. In Arabidopsis T-DNA insertion mutants that do not transcribe AtBG_ppap, functional studies showed that GFP cell-to-cell movement between epidermal cells is reduced, and the conductivity coefficient of Pd is lower. Measurements of callose levels around Pd after wounding revealed that callose accumulation in the mutant plants was higher. Taken together, we suggest that AtBG_ppap is a Pd-associated membrane protein involved in plasmodesmal callose degradation, and functions in the gating of Pd.

Grain setting defect1, Encoding a Remorin Protein, Affects the Grain Setting in Rice through Regulating Plasmodesmatal Conductance

“…The uneven distribution of signals colocalized with aniline blue-stained callose (Fig. 7, B and C), suggesting that GSD1 is associated with PD structure (Levy et al, 2007). The plasmolysis assay showed that the GFP signal was localized on the retracted PM and Hechtian strands (Fig.…”

“…For example, actin and myosin, which link the desmotubule to the plasma membrane (PM) at the neck region of PD, are believed to play a role in regulating PD permeability by controlling PD aperture (White et al, 1994;Ding et al, 1996;Reichelt et al, 1999). Callose deposition can also impact the size of the PD aperture at the neck region (Radford et al, 1998;Levy et al, 2007) and callose synthase genes such as Glucan SynthaseLike7 (GSL7, also named CalS7), GSL8, and GSL12 have been shown to play a role in regulating symplastic trafficking (Guseman et al, 2010;Barratt et al, 2011;Vatén et al, 2011;Xie et al, 2011). Other proteins that have been shown to impact the structure and function of the PD include glycosylphosphatidylinositol (GPI)-anchored proteins, PD callose binding protein1 (PDCB1), which is also associated with callose deposition (Simpson et al, 2009), and LYSIN MOTIF DOMAIN-CONTAINING GLYCOSYLPHOSPHATIDYLINOSITOL-ANCHORED PROTEIN2, which limits the molecular flux through the PD by chitin perception (Faulkner et al, 2013).…”

Callose Synthase GSL7 Is Necessary for Normal Phloem Transport and Inflorescence Growth in Arabidopsis

“…It is also possible that GSL7 is involved in callose turnover in mature sieve plate pores in intact plants. Turnover of callose deposits in the neck regions of plasmodesmata is proposed to alter the diameter of the plasmodesmatal pore and thus control plasmodesmatal fluxes (Levy et al, 2007). Similarly, turnover of callose in the sieve plate pore in response to developmental and/or environmental factors may alter the diameter of the pore and thus modulate phloem conductivity.…”

Plant- and stimulus-specific variations in remote-controlled sieve-tube occlusion

“…PD constriction is reached by Ca 2+ -dependent 9 deposition of β-1,3-glucane polymers (callose) into the apoplast, caused by activation of membrane-associated callose synthase (β-1,3-glucan synthase); PD re-opening is achieved by a callose-degrading membrane-associated β-1,3-glucanase. 10 In complement sieve-tubes are occluded by structural 7,4 or, possibly, water-soluble proteins 11 ( Fig. 1).…”