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Role of callose synthases in transfer cell wall development in tocopherol deficient Arabidopsis mutants.

Maeda H, Song W, Sage T, Dellapenna D - Front Plant Sci (2014)

Bottom Line: However, introduction of gsl4 or gsl11 mutations individually into the vte2 background did not suppress callose deposition or the overall LT-induced phenotypes of vte2.Intriguingly, introduction of a mutation disrupting GSL5, the major GSL responsible for pathogen-induced callose deposition, into vte2 substantially reduced vascular callose deposition at LT, but again had no effect on the photoassimilate export phenotype of LT-treated vte2.These results suggest that GSL5 plays a major role in TCW callose deposition in LT-treated vte2 but that this GSL5-dependent callose deposition is not the primary cause of the impaired photoassimilate export phenotype.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, Michigan State University East Lansing, MI, USA ; Cell and Molecular Biology Program, Michigan State University East Lansing, MI, USA ; Department of Botany, University of Wisconsin-Madison Madison, WI, USA.

ABSTRACT
Tocopherols (vitamin E) are lipid-soluble antioxidants produced by all plants and algae, and many cyanobacteria, yet their functions in these photosynthetic organisms are still not fully understood. We have previously reported that the vitamin E deficient 2 (vte2) mutant of Arabidopsis thaliana is sensitive to low temperature (LT) due to impaired transfer cell wall (TCW) development and photoassimilate export associated with massive callose deposition in transfer cells of the phloem. To further understand the roles of tocopherols in LT induced TCW development we compared the global transcript profiles of vte2 and wild-type leaves during LT treatment. Tocopherol deficiency had no significant impact on global gene expression in permissive conditions, but significantly affected expression of 77 genes after 48 h of LT treatment. In vte2 relative to wild type, genes associated with solute transport were repressed, while those involved in various pathogen responses and cell wall modifications, including two members of callose synthase gene family, GLUCAN SYNTHASE LIKE 4 (GSL4) and GSL11, were induced. However, introduction of gsl4 or gsl11 mutations individually into the vte2 background did not suppress callose deposition or the overall LT-induced phenotypes of vte2. Intriguingly, introduction of a mutation disrupting GSL5, the major GSL responsible for pathogen-induced callose deposition, into vte2 substantially reduced vascular callose deposition at LT, but again had no effect on the photoassimilate export phenotype of LT-treated vte2. These results suggest that GSL5 plays a major role in TCW callose deposition in LT-treated vte2 but that this GSL5-dependent callose deposition is not the primary cause of the impaired photoassimilate export phenotype.

No MeSH data available.


Related in: MedlinePlus

A proposed model of the timing of biochemical changes in LT-induced phenotypes of tocopherol-deficient mutants. Tocopherol deficiency, e.g., by the vte2 mutation, leads to constitutive alterations in the fatty acid composition of endoplasmic reticulum (ER) membrane lipids [i.e., reduced linolenic acid (18:3) and increased linoleic acid (18:2)]. These alterations are suppressed by the mutation of the ER FATTY ACID DESATURASE 2 gene (fad2), which also suppresses all of the LT-induced vte2 phenotypes (Maeda et al., 2008; Song et al., 2010). Subsequent vasculature-specific callose deposition is primarily mediated by the GSL5 enzyme and tocopherol-deficiency affects its activity post-transcriptionally. Although low levels of GSL5-independent callose deposition still occurs, loss of the massive GSL5-dependent callose deposition in transfer cells does not affected the subsequent defect in photoassimilate export in LT-treated vte2.
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Figure 7: A proposed model of the timing of biochemical changes in LT-induced phenotypes of tocopherol-deficient mutants. Tocopherol deficiency, e.g., by the vte2 mutation, leads to constitutive alterations in the fatty acid composition of endoplasmic reticulum (ER) membrane lipids [i.e., reduced linolenic acid (18:3) and increased linoleic acid (18:2)]. These alterations are suppressed by the mutation of the ER FATTY ACID DESATURASE 2 gene (fad2), which also suppresses all of the LT-induced vte2 phenotypes (Maeda et al., 2008; Song et al., 2010). Subsequent vasculature-specific callose deposition is primarily mediated by the GSL5 enzyme and tocopherol-deficiency affects its activity post-transcriptionally. Although low levels of GSL5-independent callose deposition still occurs, loss of the massive GSL5-dependent callose deposition in transfer cells does not affected the subsequent defect in photoassimilate export in LT-treated vte2.

Mentions: The biochemical phenotype of 48 h-LT-treated vte2 plants includes phloem transfer cell-specific callose deposition that spreads from the petiole to the upper part of the mature leaves and potentially impacts the capacity of source to sink photoassimilate transportation (Maeda et al., 2006). Consistent with these phenotypes, the expression of several genes (e.g., glycosyl transferases, glucanases) that are potentially involved in cell wall polymer modification in transfer cells (Dibley et al., 2009) were significantly upregulated in vte2 (Table 1). We also assessed the molecular nature of vasculature specific callose deposition observed in LT-treated vte2 and its impact on the photoassimilate export phenotype. Based on our microarray analysis GSL4 and GSL11 were more strongly upregulated in LT-treated vte2 than in Col (Supplemental Figure S5) and therefore considered likely candidates for enzymes mediating the massive callose deposition observed in LT-treated vte2. However, introduction of gsl4 and gsl11 mutations into the vte2 background did not visibly alter the callose deposition or overall phenotypes in LT-induced gsl4 vte2 or gsl11 vte2 double mutants (Figure 4). Somewhat surprisingly, though GSL5 was not differentially expressed in LT-treated vte2 and Col (Supplemental Figure S5), knocking out GSL5 in the vte2 background eliminated the majority, but not all, of callose deposition in LT-treated vte2 (Figures 5A and 7), indicating that the bulk of vte2 callose deposition at LT is GSL5-dependent (Figure 7). Because GSL5 is also responsible for callose deposition in response to wounding (Jacobs et al., 2003), tocopherol deficiency may improperly stimulate the wound response pathway in transfer cells and lead to post-transcriptional activation of the GSL5 enzyme in transfer cells. However, Col and vte2 showed similar levels of wound-induced callose deposition (data not shown). Taken together, these data suggest that tocopherols are required for post-transcriptional activation of GSL5 in transfer cells by a mechanism that is likely independent of the wound-signaling pathway.


Role of callose synthases in transfer cell wall development in tocopherol deficient Arabidopsis mutants.

Maeda H, Song W, Sage T, Dellapenna D - Front Plant Sci (2014)

A proposed model of the timing of biochemical changes in LT-induced phenotypes of tocopherol-deficient mutants. Tocopherol deficiency, e.g., by the vte2 mutation, leads to constitutive alterations in the fatty acid composition of endoplasmic reticulum (ER) membrane lipids [i.e., reduced linolenic acid (18:3) and increased linoleic acid (18:2)]. These alterations are suppressed by the mutation of the ER FATTY ACID DESATURASE 2 gene (fad2), which also suppresses all of the LT-induced vte2 phenotypes (Maeda et al., 2008; Song et al., 2010). Subsequent vasculature-specific callose deposition is primarily mediated by the GSL5 enzyme and tocopherol-deficiency affects its activity post-transcriptionally. Although low levels of GSL5-independent callose deposition still occurs, loss of the massive GSL5-dependent callose deposition in transfer cells does not affected the subsequent defect in photoassimilate export in LT-treated vte2.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3928550&req=5

Figure 7: A proposed model of the timing of biochemical changes in LT-induced phenotypes of tocopherol-deficient mutants. Tocopherol deficiency, e.g., by the vte2 mutation, leads to constitutive alterations in the fatty acid composition of endoplasmic reticulum (ER) membrane lipids [i.e., reduced linolenic acid (18:3) and increased linoleic acid (18:2)]. These alterations are suppressed by the mutation of the ER FATTY ACID DESATURASE 2 gene (fad2), which also suppresses all of the LT-induced vte2 phenotypes (Maeda et al., 2008; Song et al., 2010). Subsequent vasculature-specific callose deposition is primarily mediated by the GSL5 enzyme and tocopherol-deficiency affects its activity post-transcriptionally. Although low levels of GSL5-independent callose deposition still occurs, loss of the massive GSL5-dependent callose deposition in transfer cells does not affected the subsequent defect in photoassimilate export in LT-treated vte2.
Mentions: The biochemical phenotype of 48 h-LT-treated vte2 plants includes phloem transfer cell-specific callose deposition that spreads from the petiole to the upper part of the mature leaves and potentially impacts the capacity of source to sink photoassimilate transportation (Maeda et al., 2006). Consistent with these phenotypes, the expression of several genes (e.g., glycosyl transferases, glucanases) that are potentially involved in cell wall polymer modification in transfer cells (Dibley et al., 2009) were significantly upregulated in vte2 (Table 1). We also assessed the molecular nature of vasculature specific callose deposition observed in LT-treated vte2 and its impact on the photoassimilate export phenotype. Based on our microarray analysis GSL4 and GSL11 were more strongly upregulated in LT-treated vte2 than in Col (Supplemental Figure S5) and therefore considered likely candidates for enzymes mediating the massive callose deposition observed in LT-treated vte2. However, introduction of gsl4 and gsl11 mutations into the vte2 background did not visibly alter the callose deposition or overall phenotypes in LT-induced gsl4 vte2 or gsl11 vte2 double mutants (Figure 4). Somewhat surprisingly, though GSL5 was not differentially expressed in LT-treated vte2 and Col (Supplemental Figure S5), knocking out GSL5 in the vte2 background eliminated the majority, but not all, of callose deposition in LT-treated vte2 (Figures 5A and 7), indicating that the bulk of vte2 callose deposition at LT is GSL5-dependent (Figure 7). Because GSL5 is also responsible for callose deposition in response to wounding (Jacobs et al., 2003), tocopherol deficiency may improperly stimulate the wound response pathway in transfer cells and lead to post-transcriptional activation of the GSL5 enzyme in transfer cells. However, Col and vte2 showed similar levels of wound-induced callose deposition (data not shown). Taken together, these data suggest that tocopherols are required for post-transcriptional activation of GSL5 in transfer cells by a mechanism that is likely independent of the wound-signaling pathway.

Bottom Line: However, introduction of gsl4 or gsl11 mutations individually into the vte2 background did not suppress callose deposition or the overall LT-induced phenotypes of vte2.Intriguingly, introduction of a mutation disrupting GSL5, the major GSL responsible for pathogen-induced callose deposition, into vte2 substantially reduced vascular callose deposition at LT, but again had no effect on the photoassimilate export phenotype of LT-treated vte2.These results suggest that GSL5 plays a major role in TCW callose deposition in LT-treated vte2 but that this GSL5-dependent callose deposition is not the primary cause of the impaired photoassimilate export phenotype.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, Michigan State University East Lansing, MI, USA ; Cell and Molecular Biology Program, Michigan State University East Lansing, MI, USA ; Department of Botany, University of Wisconsin-Madison Madison, WI, USA.

ABSTRACT
Tocopherols (vitamin E) are lipid-soluble antioxidants produced by all plants and algae, and many cyanobacteria, yet their functions in these photosynthetic organisms are still not fully understood. We have previously reported that the vitamin E deficient 2 (vte2) mutant of Arabidopsis thaliana is sensitive to low temperature (LT) due to impaired transfer cell wall (TCW) development and photoassimilate export associated with massive callose deposition in transfer cells of the phloem. To further understand the roles of tocopherols in LT induced TCW development we compared the global transcript profiles of vte2 and wild-type leaves during LT treatment. Tocopherol deficiency had no significant impact on global gene expression in permissive conditions, but significantly affected expression of 77 genes after 48 h of LT treatment. In vte2 relative to wild type, genes associated with solute transport were repressed, while those involved in various pathogen responses and cell wall modifications, including two members of callose synthase gene family, GLUCAN SYNTHASE LIKE 4 (GSL4) and GSL11, were induced. However, introduction of gsl4 or gsl11 mutations individually into the vte2 background did not suppress callose deposition or the overall LT-induced phenotypes of vte2. Intriguingly, introduction of a mutation disrupting GSL5, the major GSL responsible for pathogen-induced callose deposition, into vte2 substantially reduced vascular callose deposition at LT, but again had no effect on the photoassimilate export phenotype of LT-treated vte2. These results suggest that GSL5 plays a major role in TCW callose deposition in LT-treated vte2 but that this GSL5-dependent callose deposition is not the primary cause of the impaired photoassimilate export phenotype.

No MeSH data available.


Related in: MedlinePlus