Abstract
Background: As a xerophytic shrub, forming developed root system dominated with lateral roots is one of the effective strategies for Zygophyllum xanthoxylum to adapt to desert habitat. However, the molecular mechanism of lateral root formation in Z. xanthoxylum is still unclear. Auxin response factors (ARFs) are a master family of transcription factors (TFs) in auxin-mediated biological processes including root growth and development. Results: Here, to determine the relationship between ARFs and root system formation in Z. xanthoxylum, a total of 30 potential ZxARF genes were first identified, and their classifications, evolutionary relationships, duplication events and conserved domains were characterized. 107 ARF protein sequences from alga to higher plant species including Z. xanthoxylum are split into A, B, and C 3 Clades, consisting with previous studies. The comparative analysis of ARFs between xerophytes and mesophytes showed that A-ARFs of xerophytes expanded considerably more than that of mesophytes. Furthermore, in this Clade, ZxARF5b and ZxARF8b have lost the important B3 DNA-binding domain partly and completely, suggesting both two proteins may be more functional in activating transcription by dimerization with AUX/IAA repressors. qRT-PCR results showed that all A-ZxARFs are high expressed in the roots of Z. xanthoxylum, and they were significantly induced by drought stress. Among these A-ZxARFs, the over-expression assay showed that ZxARF7c and ZxARF7d play positive roles in lateral root formation. Conclusion: This study provided the first comprehensive overview of ZxARFs and highlighted the importance of A-ZxARFs in the lateral root development.