Salt tolerance of Arabidopsis thaliana requires maturation of N -glycosylated proteins in the Golgi apparatus

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Abstract
Protein N -glycosylation in the endoplasmic reticulum (ER) and in the Golgi apparatus is an essential process in eukaryotic cells. Although the N -glycosylation pathway in the ER has been shown to regulate protein quality control, salt tolerance, and cellulose biosynthesis in plants, no biological roles have been linked functionally to N -glycan modifications that occur in the Golgi apparatus. Herein, we provide evidence that mutants defective in N -glycan maturation, such as complex glycan 1 ( cgl1 ), are more salt-sensitive than wild type. Salt stress caused growth inhibition, aberrant root-tip morphology, and callose accumulation in cgl1 , which were also observed in an ER oligosaccharyltransferase mutant, staurosporin and temperature sensitive 3a ( stt3a ). Unlike stt3a , cgl1 did not cause constitutive activation of the unfolded protein response. Instead, aberrant modification of the plasma membrane glycoprotein KORRIGAN 1/RADIALLY SWOLLEN 2 (KOR1/RSW2) that is necessary for cellulose biosynthesis occurred in cgl1 and stt3a . Genetic analyses identified specific interactions among rsw2 , stt3a , and cgl1 mutations, indicating that the function of KOR1/RSW2 protein depends on complex N -glycans. Furthermore, cellulose deficient rsw1-1 and rsw2-1 plants were also salt-sensitive. These results establish that plant protein N -glycosylation functions beyond protein folding in the ER and is necessary for sufficient cell-wall formation under salt stress.