Genome-Wide Identification and Genetic Characterization of Eucommia ulmoides NAC Family Genes and Functional Analysis of EuNAC9 in Relieving Mn2+ Stress

NAC (NAM/ATAF1,2/CUC2) is one of the most important plant-specific transcription factors, playing a significant role in plant growth, morphogenesis, and stress resilience. In this investigation, 77 members of the NAC gene family were identified from the Eucommia ulmoides  database, and these E. ulmoides  NAC families were classified into 18 subfamilies based on their protein sequences. Currently, the architectural design, conserved domains, and cis -acting elements of EuNAC  genes, as well as physicochemical properties of EuNAC proteins, have also been analyzed. In addition, the expression patterns of selected EuNAC  genes under five heavy metal (Cu 2+ , Cd 2+ , Pb 2+ , Mn 2+ , and As 5+ ) imposed stresses were investigated. The results showed that the expression of EuNAC9 experienced a significant induction to upregulate under these five heavy metal stresses, suggesting that EuNAC9  may mediate the response to these five heavy metal stresses. In addition, the function of EuNAC9  was investigated in both transgenic yeasts and tobaccos. The transgenic yeasts exhibited enhanced resistance to Mn 2+  stress by increasing the expression of ScSMF1  and ScSOD2 , whereas the transgenic tobacco grew better under Mn 2+  stress and showed intense antioxidant enzyme activity to alleviate the accumulation of H 2 O 2 and O 2 − . Moreover, subcellular localization indicated EuNAC9 was a nuclear localization protein, and the transcriptional activity domain of EuNAC9 resided at the C-terminal. This study will provide a theoretical framework for analyzing the molecular regulatory mechanisms of plant responses to heavy metals mediated by EuNAC9  genes and elucidating the biological roles of E. ulmoides  NACs in responding to heavy metal stress.