Mulberry ERF Transcription Factor MnERF23 Is a Positive Regulator of Plant Drought Tolerance

Mulberry (Morus alba L.) is an important economic tree species, and its leaves are increasingly being used to prepare healthy dishes in addition to serving as food for silkworms. Drought is one of the main stress factors affecting the quality of mulberry leaves; however, the molecular mechanisms through which mulberry plants respond to drought stress are currently unclear. The AP2/ERF gene family is involved in plant growth, development and stress response processes. In response to drought stress, the expression of mulberry MnERF23 is induced. The overexpression of MnERF23 in Arabidopsis thaliana enhances drought tolerance, increases root length, and activates the expression of stress-related genes in transgenic plants. The transient overexpression of MnERF23 in mulberry leaves can reduce stress-related damage in transgenic seedlings and promote better growth. In this study, RNA-seq analysis of mulberry leaves transiently overexpressing MnERF23 in both normal and drought environments revealed 470 and 687 DEGs, respectively. In the DS-1305 vs. DS-ERF23 comparison, genes related to ROS clearance, cell wall precursors, and lignin synthesis were up-regulated. Further analysis revealed that Mn4CL3 is an up-regulated differentially expressed gene and that the promoter retains a DRE/CRT cis-acting element. The Y1H and dual-luciferase assay results reveal that MnERF23 can positively regulate Mn4CL3 in combination with DRE/CRT, synergistically enhancing the drought tolerance of mulberry. We elucidated the regulatory mechanism through which MnERF23-dependent DRE/CRT cis-acting elements promote Mn4CL3 expression and enhance drought tolerance in mulberry. This study contributes to the theoretical research on the regulatory network of plant abiotic stress, providing a theoretical basis and technical support for forest genetic breeding.