Abstract
Xyloglucan is a quantitatively major polysaccharide in the primary cell walls of flowering plants and has been reported to affect plants’ ability to tolerate toxic elements. However, it is not known if altering the amounts of xyloglucan in the wall influences the uptake and translocation of inorganic arsenic (As). Here, we identified two Nicotiana tabacum genes that encode xyloglucan-specific xylosyltransferases (XXT), which we named NtXXT1 and NtXXT2. We used CRISPR-Cas9 technology to generate ntxxt1, ntxxt2, and ntxxt1/2 mutant tobacco plants to determine if preventing xyloglucan synthesis affects plant growth and their ability to accumulate As. We show that NtXXT1 and NtXXT2 are required for xyloglucan biosynthesis because no discernible amounts of xyloglucan were present in the cell walls of the ntxxt1/2 double mutant. The tobacco double mutant (ntxxt1/2) and the corresponding Arabidopsis mutant (atxxt1/2) do not have severe growth defects but do have a short root hair phenotype and a slow growth rate. This phenotype is rescued by overexpressing NtXXT1 or NtXXT2 in atxxt1/2. Growing ntxxt mutants in the presence of AsIII or AsV showed that the absence of cell wall xyloglucan affects the accumulation and translocation of As. Most notably, root retention of As increased substantially and the amounts of As translocated to the shoots decreased in ntxxt1/2. Our results suggest that xyloglucan-deficient plants provide a strategy for the phytoremediation of As contaminated soils.
Highlights
The polysaccharide-rich cell wall is plants’ first line of defense against toxic elements present in soils and water as it may prevent them from entering the cytoplasm (Parrotta et al, 2015)
A total of 11 putative xyloglucan-specific xylosyltransferases (XXT) genes were identified in the N. tabacum L. genome
Our results have demonstrated that tobacco plants lacking both NtXXT1 and NtXXT2 have growth and root hair phenotypes and wall chemotypes that are similar to the Arabidopsis xxt1/2 mutant plant
Summary
The polysaccharide-rich cell wall is plants’ first line of defense against toxic elements present in soils and water as it may prevent them from entering the cytoplasm (Parrotta et al, 2015). Increases in pectin and hemicellulose in rice leaves have been reported to be responsible for increased Cd2+ accumulation in root cell walls and a decrease in soluble Cd2+ (Xiong et al, 2009). A decrease of pectin and hemicelluloses resulting from phosphorous deficiency has been reported to enhance Cd2+ exclusion in Arabidopsis root walls (Zhu et al, 2012a). Cd2+ tolerance in tobacco has been increased by overexpressing a Populus euphratica gene encoding a xyloglucan (XyG) endotransglucosylase/hydrolase (XTH) to decrease the amount of wall XyG (Han et al, 2014). A decrease of XyG (xth mutant; Han et al, 2014) or the absence of XyG (xxt1/2 double mutant; Zhu et al, 2012b) reduces the accumulation of the “a” class hard metal aluminum (Al) in Arabidopsis root cell walls. The Al-binding capacity is determined in part by the extent of XyG O-acetylation, since more Al accumulates in the walls of Arabidopsis XyG O-acetyltransferase mutants than their wild-type counterpart (Zhu et al, 2014)
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