Abstract
Although xyloglucan (XyG) is reported to bind Aluminium (Al), the influence of XyG fucosylation on the cell wall Al binding capacity and plant Al stress responses is unclear. We show that Arabidopsis T-DNA insertion mutants with reduced AXY3 (XYLOSIDASE1) function and consequent reduced levels of fucosylated XyG are more sensitive to Al than wild-type Col-0 (WT). In contrast, T-DNA insertion mutants with reduced AXY8 (FUC95A) function and consequent increased levels of fucosylated XyG are more Al resistant. AXY3 transcript levels are strongly down regulated in response to 30 min Al treatment, whilst AXY8 transcript levels also repressed until 6 h following treatment onset. Mutants lacking AXY3 or AXY8 function exhibit opposing effects on Al contents of root cell wall and cell wall hemicellulose components. However, there was no difference in the amount of Al retained in the pectin components between mutants and WT. Finally, whilst the total sugar content of the hemicellulose fraction did not change, the altered hemicellulose Al content of the mutants is shown to be a likely consequence of their different XyG fucosylation levels. We conclude that variation in XyG fucosylation levels influences the Al sensitivity of Arabidopsis by affecting the Al-binding capacity of hemicellulose.
Highlights
To cause damage to plant roots, Al must first enter the cellular cytosol
Because XyG is a major component of cell wall hemicellulose and the major Al binding site of the Arabidopsis cell wall[16], we determined the effect of Al treatment on root cell wall XyG content
MALDI-TOF analysis after xyloglucanase digestion indicated that some xyloglucanase-accessible XyG repeat-units, especially XXG, XLG, XFG and XXLG, were increased significantly following growth for 24 hours in Al stress conditions (Fig. 1), meaning that there are more side chains in XyG when subjected to Al stress
Summary
To cause damage to plant roots, Al must first enter the cellular cytosol. Axy[8] mutants, having reduced fucosidase function, exhibit increased XyG fucosylation[19] (http://paulylab.berkeley.edu/ axy-mutants.html) These changes in XyG fucosylation (in either axy[3] or axy[8] mutants) confer no change in visible growth or morphological phenotypes[19]. Whilst both XET and expansins have previously been demonstrated to be involved in plant responses to Al stress[15,30], the possibility that modification of XyG structure alters plant Al stress responses remains to be investigated. We characterize the responses of AXY3 and AXY8 to Al stress, and show that modulation of the XyG fucosylation level by AXY3 and AXY8 changes the Al binding capacity of hemicellulose, which is the major contributor to Al retention in the Arabidopsis cell wall
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