Molecular characterization and expression analysis of the SPL gene family with BpSPL9 transgenic lines found to confer tolerance to abiotic stress in Betula platyphylla Suk

SQUAMOSA promoter binding protein-like (SPL) genes encode plant-specific transcription factors and play vital roles in plant growth and development. The BpSPL gene family has not been systematically studied in Betula platyphylla Suk. (birch). In this study, we identified 12 full-length BpSPLs and analyzed their gene structure and distribution patterns in the birch genome. The phylogenetic analysis of SPLs in different plants species revealed six groups. Furthermore, seven of the 12 BpSPLs contained miR156 recognition sites. Comparative analysis of the spatiotemporal expression patterns of BpSPLs and miR156 uncovered an inverse relationship, suggesting a regulatory role for miR156-SPL circuits. We showed that the expression of BpSPL9 was induced by NaCl and PEG6000 stresses in roots and leaves. Through transgenic experiments, we obtained 18 independent lines with ectopic expression of BpSPL9. Moreover, physiological and enzymatic analyses of transgenic lines revealed improved scavenging of ROS to salt and drought stress. Our results will provide useful information for elucidating the biological functions of SPLs in B. platyphylla with potential applications in improving scavenging of ROS.