Ectopic expression of Medicago truncatula homeodomain finger protein, MtPHD6, enhances drought tolerance in Arabidopsis

Background: The plant homeodomain (PHD) finger is a Cys(4)HisCys(3)-type zinc finger which promotes protein-protein interactions and binds to the cis-acting elements in the promoter regions of target genes. In Medicago truncatula, five PHD homologues with full-length sequence were identified. However, the detailed function of PHD genes was not fully addressed. Results: In this study, we characterized the function of MtPHD6 during plant responses to drought stress. MtPHD6 was highly induced by drought stress. Ectopic expression of MtPHD6 in Arabidopsis enhanced tolerance to osmotic and drought stresses. MtPHD6 transgenic plants exhibited decreased water loss rate, MDA and ROS contents, and increased leaf water content and antioxidant enzyme activities under drought condition. Global transcriptomic analysis revealed that MtPHD6 reprogramed transcriptional networks in transgenic plants. Expression levels of ABA receptor PYR/PYLs, ZINC FINGER, AP2/EREBP and WRKY transcription factors were mainly up-regulated after transformation of MtPHD6. Interaction network analysis showed that ZINC FINGER, AP2/EREBP and WRKY interacted with each other and downstream stress induced proteins. Conclusions: We proposed that ZINC FINGER, AP2/EREBP and WRKY transcription factors were activated through ABA dependent and independent pathways to increase drought tolerance of MtPHD6 transgenic plants.