Abstract
Freezing triggers extracellular ice formation leading to cell dehydration and deformation during a freeze-thaw cycle. Many plant species increase their freezing tolerance during exposure to low, non-freezing temperatures, a process termed cold acclimation. In addition, exposure to mild freezing temperatures after cold acclimation evokes a further increase in freezing tolerance (sub-zero acclimation). Previous transcriptome and proteome analyses indicate that cell wall remodelling may be particularly important for sub-zero acclimation. In the present study, we used a combination of immunohistochemical, chemical and spectroscopic analyses to characterize the cell walls of Arabidopsis thaliana and characterized a mutant in the XTH19 gene, encoding a xyloglucan endotransglucosylase/hydrolase (XTH). The mutant showed reduced freezing tolerance after both cold and sub-zero acclimation, compared to the Col-0 wild type, which was associated with differences in cell wall composition and structure. Most strikingly, immunohistochemistry in combination with 3D reconstruction of centres of rosette indicated that epitopes of the xyloglucan-specific antibody LM25 were highly abundant in the vasculature of Col-0 plants after sub-zero acclimation but absent in the XTH19 mutant. Taken together, our data shed new light on the potential roles of cell wall remodelling for the increased freezing tolerance observed after low temperature acclimation.
Highlights
Freezing is a severe stress for plants, which is accompanied by a phase transition from liquid water to ice crystals in the tissues
We focus on xyloglucan, a primary component of hemicellulose of dicots, and the gene XTH19 encoding a xyloglucan-modifying enzyme
We evaluate the freezing tolerance of T-DNA insertion mutants of the four closely related genes XTH17 to XTH20 under different acclimation conditions and provide detailed analysis of cell wall composition and properties of the xth19 mutant
Summary
Freezing is a severe stress for plants, which is accompanied by a phase transition from liquid water to ice crystals in the tissues. The XTH19 gene was identified as SZA-induced in a previous study (Le et al, 2015) In this context, we evaluate the freezing tolerance of T-DNA insertion mutants of the four closely related genes XTH17 to XTH20 under different acclimation conditions and provide detailed analysis of cell wall composition and properties of the xth mutant. Our results suggest that the compositional and architectural/organizational changes of the cell wall observed after both CA and SZA may play a role for increasing freezing tolerance and highlight the functional role of XTH19 via xyloglucan remodelling in these cell wall responses
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