Cadmium (Cd), a highly mobile and phytotoxic heavy metal, threatens plant growth and food safety and has increased interest in woody plant-based phytoremediation. However, the genome-wide characteristics of the NAC transcription factor family and its role in Cd tolerance remain largely unknown in pomegranate (Punica granatum L.), a stress-tolerant woody plant. In this study, 121 PgNAC genes were identified from the chromosome-level genome of the pomegranate cultivar ‘Tunisia’. Phylogenetic analysis classified these genes into two major groups and 16 subgroups. PgNAC genes were unevenly distributed across the eight chromosomes and showed evident clustered distribution patterns. Synteny and Ka/Ks analyses further revealed that segmental and tandem duplication jointly shaped the expansion of the PgNAC family, while the duplicated pairs have largely evolved under strong purifying selection. Conserved motif and gene structure analyses showed that PgNAC proteins possessed a highly conserved N-terminal NAM domain, whereas their C-terminal regions were relatively divergent. Promoter analysis further identified abundant hormone- and stress-responsive cis-elements, suggesting diverse regulatory roles of the PgNAC family. Transcriptome profiling identified PgNAC87, a member of the NAP subfamily, as a Cd-responsive candidate gene that was consistently upregulated in both roots and leaves under Cd stress. Heterologous overexpression of PgNAC87 in tobacco significantly enhanced Cd tolerance, as reflected by alleviated growth inhibition, increased antioxidant enzyme activities and osmotic adjustment substances, and reduced oxidative damage. Collectively, our results clarify the evolutionary features of the PgNAC family and its involvement in Cd-induced transcriptional regulation, while highlighting PgNAC87 as a potential genetic target for enhancing Cd tolerance in pomegranate and related woody species.
Ren et al. (Sat,) studied this question.