The B-box proteins (BBXs) are zinc finger proteins containing one or two B-box domain(s) and involved in regulation of development processes as transcription factors in plants. Here, seven BBX genes in Malus domestica genome (MdBBXs) were identified and found to be up-regulated under abiotic stresses, with 2-12 folds in roots. All recombinant MdBBXs expressed in Escherichia coli (E. coli) enhanced the cell's tolerance to salt and osmotic stresses, respectively. Deficiency of B-box domain of MdBBX10 led to the loss of anti-stress functions. Five conservative cysteines in B-box domain played crucial roles in stress resistance, which are involved in two of metal iron binding sites of zinc finger motifs in BBXs. All the above results suggested MdBBXs confer stress tolerance to E. coli cell against abiotic stresses.
Keywords: B-box domain; Conservative cysteine; Stress tolerance; Zinc finger motifs.