BackgroundZygophyllum xanthoxylum is a constructive species in the desert region. Forming a massive root system to absorb water and nutrients from soil is an effective strategy for Z. xanthoxylum to survive. However, the molecular mechanisms of its root development and stress tolerance are poorly understood. SMALL AUXIN UP RNAs (SAURs) belong to early auxin-responsive genes and play important roles in plant growth and development as well as stress responses.MethodsA bioinformatics analysis of the ZxSAURs family was conducted and the function of ZxSAUR15 in root development and stress response was investigated using ZxSAUR15-overexpressing Arabidopsis and ZxSAUR15-RNAi Z. xanthoxylum.Results87 ZxSAUR genes were identified. Among them, there are 56 segmental and 7 tandem duplication events, which caused the expansion of this gene family. Various abiotic responsive elements are located in the promoter regions of ZxSAURs, and most of their expression levels in root change in respond to salt and osmotic treatments. In addition, overexpression of ZxSAUR15 promoted the root growth as well as salt and osmotic stress tolerance of Arabidopsis. While silencing of ZxSAUR15 leads to growth inhibition on Z. xanthoxylum and its higher sensitivity to salt and osmotic stress, which are associated with the plasma membrane (PM) H+-ATPase-mediated H+ efflux and ion homeostasis.ConclusionTogether, these results demonstrate that ZxSAUR family, particularly ZxSAUR15, plays important roles in root growth and response to abiotic stress, laying a foundation for deciphering the molecular mechanisms underlying desert plants' adaptation to harsh environment.