Plasmodesmata without callose and calreticulin in higher plants – open channels for fast symplastic transport?

Abstract

Plasmodesmata (PD) represent membrane-lined channels that link adjacent plant cells across the cell wall. PD of higher plants contain a central tube of endoplasmic reticulum (ER) called desmotubule. Membrane and lumen proteins seem to be able to move through the desmotubule, but most transport processes through PD occur through the cytoplasmic annulus (Brunkard etal., 2013). Calreticulin (CRT), a highly conserved Ca2+-binding protein found in all multicellular eukaryotes, predominantly located in the ER, was shown to localize to PD, though not all PD accumulate CRT. In nitrogen-fixing actinorhizal root nodules of the Australian tree Casuarina glauca, the primary walls of infected cells containing the microsymbiont become lignified upon infection. TEM analysis of these nodules showed that during the differentiation of infected cells, PD connecting infected cells, and connecting infected and adjacent uninfected cells, were reduced in number as well as diameter (Schubert etal., 2013). In contrast with PD connecting young infected cells, and most PD connecting mature infected and adjacent uninfected cells, PD connecting mature infected cells did not accumulate CRT. Furthermore, as shown here, these PD were not associated with callose, and based on their diameter, they probably had lost their desmotubules. We speculate that either this is a slow path to PD degradation, or that the loss of callose accumulation and presumably also desmotubules leads to the PD becoming open channels and improves metabolite exchange between cells.

Comparative proteomic analysis of Phalaenopsis leaves in the vegetative and flowering phase

“…Calreticulin and calmodulin, versatile calcium signaling transducers (Perochon et al 2011;Demchenko et al 2014), were decreased in abundance in Phalaenopsis leaves in the flowering phase in this study; whereas two signaling proteins, rapid alkalinization factors (RALF) and Ras-related protein RABB1c, were increased in the flowering phase. RALF active peptide hormones are considered to play important roles in plant development (Murphy and De Smet 2014).…”

Combined microscopy and molecular analyses show phloem occlusions and cell wall modifications in tomato leaves in response to ‘Candidatus Phytoplasma solani’

“…At the CC–PPC interface, callose was also not detected on the plasmodesmata, suggesting the hypothesis that symplastic connectivity in tomato is not affected by the phytoplasma infection. Open plasmodesmata improve metabolite exchange between the cells, as demonstrated in plant tissues infected with microsymbionts (Demchenko et al ., ) or nematodes (Hofmann et al ., ).…”

Late progamic phase and fertilization affect calreticulin expression in the Hyacinthus orientalis female gametophyte

“…In fact, the localization of CRT outside of the ER has been frequently reported in plant cells, specifically in the Golgi stacks and secretory vesicles (Borisjuk et al 1998 ; Navazio et al 2002 ; Lenartowska et al 2002 , 2009 ; Hsieh and Huang 2005 ; Nardi et al 2006 ; Lenartowski et al 2015 ). CRT has also been localized in the cytosol (Lenartowska et al 2002 ; Jia et al 2008 ), protein bodies/protein storage vacuoles (Torres et al 2001 ; Šamaj et al 2008 ), nucleus and nuclear envelope (Denecke et al 1995 , Napier et al 1995 , Lenartowska et al 2002 ; Lenartowski et al 2015 ), and within the plasmodesmata (Baluška et al 1999 ; Laporte et al 2003 ; Chen et al 2005 ; Lenartowska et al 2009 ; Christensen et al 2010 ; Demchenko et al 2014 ). The presence of CRT was also confirmed in the plasma membrane and small patches adjacent to the plasma membrane as well as on the cell surface and even in the cell wall (Borisjuk et al 1998 ; Lenartowska et al 2002 , 2009 ; Navazio et al 2002 ; Luczak et al 2014 ; Lenartowski et al 2015 ).…”