Identification of the NAC Transcription Factors and Their Function in ABA and Salinity Response in Nelumbo nucifera

Nelumbo nucifera Gaertn. is an important perennial aquatic herb that has high ornamental, edible, medicinal, and economic value, being widely distributed and used in China. The NAC superfamily (NAM, ATAF1/2, CUC2) plays critical roles in plant growth, development, and response to abiotic and biotic stresses. Though there have been a few reports about NAC genes in lotus, systematic analysis is still relatively lacking. The present study aimed to characterize all the NAC genes in the lotus and obtain better insights on the NnNACs in response to salt stress by depending on ABA signaling. Here, 97 NAC genes were identified by searching the whole lotus genome based on the raw HMM models of the conserved NAM domain and NAC domain. They were characterized by bioinformatics analysis and divided into 18 subgroups based on the phylogenetic tree. Cis-element analysis demonstrated that NAC genes are responsive to biotic and abiotic stresses, light, low temperature, and plant hormones. Meanwhile, NAC genes had tissue expression specificity. qRT-PCR analysis indicated that NAC genes could be upregulated or downregulated by NaCl treatment, ABA, and fluoridone. In addition, NAC016, NAC025, and NAC070, whose encoding genes were significantly induced by NaCl and ABA, were located in the nucleus. Further analysis showed the three NAC proteins had transcriptional activation capabilities. The co-expression network analysis reflected that NAC proteins may form complexes with other proteins to play a role together. Our study provides a theoretical basis for further research to be conducted on the regulatory mechanisms of salinity resistance in the lotus.