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Protoplasma. 2017 Jan;254(1):125-136. doi: 10.1007/s00709-015-0921-3. Epub 2015 Dec 17.

Characterisation of Arabidopsis calnexin 1 and calnexin 2 in the endoplasmic reticulum and at plasmodesmata.

Author information

1
School of Biological Sciences, University of Sydney, Macleay Building A12, Sydney, NSW, 2006, Australia.
2
Learning and Teaching Centre, Macquarie University, Building C3B 417, Sydney, NSW, 2109, Australia.
3
School of Biological Sciences, Flinders University, GPO Box 2100, Adelaide, SA, 5001, Australia.
4
School of Biological Sciences, University of Sydney, Macleay Building A12, Sydney, NSW, 2006, Australia. robyn.overall@sydney.edu.au.

Abstract

Calnexin (CNX) is a highly conserved endoplasmic reticulum (ER) chaperone protein. Both calnexin and the homologous ER-lumenal protein, calreticulin, bind calcium ions and participate in protein folding. There are two calnexins in Arabidopsis thaliana, CNX1 and CNX2. GUS expression demonstrated that these are expressed in most Arabidopsis tissues throughout development. Calnexin transfer DNA (T-DNA) mutant lines exhibited increased transcript abundances of a number of other ER chaperones, including calreticulins, suggesting a degree of redundancy. CNX1 and CNX2 localised to the ER membrane including that within plasmodesmata, the intercellular channels connecting plant cells. This is comparable with the previous localisations of calreticulin in the ER lumen and at plasmodesmata. However, from green fluorescent protein (GFP) diffusion studies in single and double T-DNA insertion mutant lines, as well as overexpression lines, we found no evidence that CNX1 or CNX2 play a role in intercellular transport through plasmodesmata. In addition, calnexin T-DNA mutant lines showed no change in transcript abundance of a number of plasmodesmata-related proteins. CNX1 and CNX2 do not appear to have a specific localisation or function at plasmodesmata-rather the association of calnexin with the ER is simply maintained as the ER passes through plasmodesmata.

KEYWORDS:

Calnexin; Calreticulin; Endoplasmic reticulum; Plasmodesmata

PMID:
26680228
DOI:
10.1007/s00709-015-0921-3
[Indexed for MEDLINE]

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