Genome-Wide Analysis and Cloning of the Apple Stress-Associated Protein Gene Family Reveals MdSAP15, Which Confers Tolerance to Drought and Osmotic Stresses in Transgenic Arabidopsis

Stress-associated proteins (SAPs) are novel A20/AN1 zinc finger domain-containing proteins that are now favorable targets to improve abiotic stress tolerance in plants. However, the SAP gene family and their biological functions have not been identified in the important fruit crop apple (Malus × domestica Borkh.). We conducted a genome-wide analysis and cloning of this gene family in apple and determined that the overexpression of MdSAP15 enhances drought tolerance in Arabidopsis plants. We identified 30 SAP genes in the apple genome. Phylogenetic analysis revealed two major groups within that family. Results from sequence alignments and analyses of 3D structures, phylogenetics, genomics structure, and conserved domains indicated that apple SAPs are highly and structurally conserved. Comprehensive qRT-PCR analysis found various expression patterns for MdSAPs in different tissues and in response to a water deficit. A transgenic analysis showed that the overexpression of MdSAP15 in transgenic Arabidopsis plants markedly enhanced their tolerance to osmotic and drought stresses. Our results demonstrate that the SAP genes are highly conserved in plant species, and that MdSAP15 can be used as a target gene in genetic engineering approaches to improve drought tolerance.