Arabinose biosynthesis is critical for salt stress tolerance in Arabidopsis

Summary The capability to maintain cell wall integrity is critical for plants to adapt to unfavourable conditions. l ‐Arabinose (Ara) is a constituent of several cell wall polysaccharides and many cell wall‐localised glycoproteins, but so far the contribution of Ara metabolism to abiotic stress tolerance is still poorly understood. Here, we report that mutations in the MUR 4 (also known as HSR 8 ) gene, which is required for the biosynthesis of UDP ‐Ara p in Arabidopsis, led to reduced root elongation under high concentrations of NaCl, KC l, Na NO 3 , or KNO 3 . The short root phenotype of the mur4 / hsr8 mutants under high salinity is rescued by exogenous Ara or gum arabic, a commercial product of arabinogalactan proteins ( AGP s) from Acacia senegal . Mutation of the MUR 4 gene led to abnormal cell−cell adhesion under salt stress. MUR 4 forms either a homodimer or heterodimers with its isoforms. Analysis of the higher order mutants of MUR 4 with its three paralogues, MURL , DUR , MEE 25 , reveals that the paralogues of MUR 4 also contribute to the biosynthesis of UDP ‐Ara and are critical for root elongation. Taken together, our work revealed the importance of the Ara metabolism in salt stress tolerance and also provides new insights into the enzymes involved in the UDP ‐Ara biosynthesis in plants.