A Bi-Functional Xyloglucan Galactosyltransferase Is an Indispensable Salt Stress Tolerance Determinant in Arabidopsis

Abstract

Salinity is an abiotic stress that substantially limits crop production worldwide. To identify salt stress tolerance determinants, we screened for Arabidopsis mutants that are hypersensitive to salt stress and designated these mutants as short root in salt medium (rsa). One of these mutants, rsa3-1, is hypersensitive to NaCl and LiCl but not to CsCl or to general osmotic stress. Reactive oxygen species (ROS) over-accumulate in rsa3-1 plants under salt stress. Gene expression profiling with Affymetrix microarray analysis revealed that RSA3 controls expression of many genes including genes encoding proteins for ROS detoxification under salt stress. Map-based cloning showed that RSA3 encodes a xyloglucan galactosyltransferase, which is allelic to a gene previously named MUR3/KAM1. The RSA3/MUR3/KAM1-encoded xylogluscan galactosyltransferase regulates actin microfilament organization (and thereby contributes to endomembrane distribution) and is also involved in cell wall biosynthesis. In rsa3-1, actin cannot assemble and form bundles as it does in the wild-type but instead aggregates in the cytoplasm. Furthermore, addition of phalloidin, which prevents actin depolymerization, can rescue salt hypersensitivity of rsa3-1. Together, these results suggest that RSA3/MUR3/KAM1 along with other cell wall-associated proteins plays a critical role in salt stress tolerance by maintaining the proper organization of actin microfilaments in order to minimize damage caused by excessive ROS.

Galactose-Depleted Xyloglucan Is Dysfunctional and Leads to Dwarfism in Arabidopsis

“…For example, the results of in vitro studies suggest that the decreased solubility of Gal-depleted XyG reduces its accessibility to the action of XyG endotransglucosylases/hydrolases (XTHs) that are believed to be involved in wall remodeling during cell growth (Peña et al, 2004). Li et al (2013) have reported that the expression of XTH18 is increased 2-fold in rsa3-1. Thus, the cabbage-like phenotype may result at least in part from the reduced susceptibilities of the XyG to XTH.…”

“…Both of these mutants are visibly similar to wild-type plants (Madson et al, 2003;Peña et al, 2004;Tamura et al, 2005). By contrast, mutant plants including katamari1 (kam1-1, kam1-2/mur3-7, and kam1-3/mur3-3; Tamura et al, 2005;Tedman-Jones et al, 2008), constitutive ICS1:luc expression1 (TedmanJones et al, 2008), and short root in salt medium (rsa3; Li et al, 2013), which are devoid of functional MUR3, have a dwarf cabbage-like growth phenotype with curled rosette leaves, short petioles, and endomembrane aggregates. Tamura et al (2005) have proposed that the KAM1/MUR3 protein itself, rather than its galactosyltransferase activity, is required for cell elongation and normal endomembrane organization.…”

“…S6). Li et al (2013) have reported that the roots of the mur3-1 and mur3-2 plants are somewhat less sensitive to salt stress than their rsa3-1 and kam1-3 counterparts and concluded that RSA3/MUR3/KAM1 is important in the salt stress tolerance pathway. We extend this notion by proposing that the phenotype of each mur3 mutant is determined in large part by the extent of residual xyloglucan galactosylation at the MUR3-specific position.…”

Challenges and Opportunities in Produced Water and Drilling Waste Treatment Techniques to Mitigate the Adverse Environmental Impacts

“…Salinity is an abiotic stress, which imposes ion toxicity, nutrient deficiency, osmotic stress, and oxidative stress on plants during any phase of their life cycle [10]. Likewise, the high concentration of salt changes the availability of water and nutrients for microorganisms [11].…”

“…Another example is using PW to irrigate special salt-tolerant crops and trees planted in desert. Plant's tolerance to the salt is susceptible to RSA3/MUR3/KAM1 along with other cell wall-associated proteins, found by Li et al [10]. However, so far, only small amount of the PW is treated and reused in irrigating crops, watering livestock, de-icing roads, and in aquaculture, power plants, dust suppression and fire prevention [21].…”