Genome-wide identification of NAC transcription factors in Herpetospermum pedunculosum and expression analysis under salt stress.

BACKGROUND

NAC (NAM, ATAF1/2, CUC2) transcription factors are plant-specific regulators of development and abiotic-stress adaptation, yet their properties and functions in the alpine cucurbit Herpetospermum pedunculosum remains unknown.

OBJECTIVE

This study aims to conduct a genome-wide identification and characterization of the NAC transcription factor family in H. pedunculosum and to preliminarily explore its potential functions in response to salt stress.

METHODS

NAC genes in the H. pedunculosum genome were identified, followed by analyses of their chromosomal distribution, phylogenetic relationships, gene structures, conserved motifs, and promoter cis-elements, and Gene Ontology (GO) annotation. Their expression patterns were analyzed using transcriptome data from salt stress conditions, and eight salt-responsive genes were validated by RT-qPCR. Finally, the subcellular localization of a representative candidate gene, HpNAC33, was determined experimentally.

RESULTS

A total of 80 HpNAC genes were identified, distributed unevenly across 10 chromosomes, and classified them into 16 subfamilies based on phylogenetic analysis. The promoter analyses revealed extensive cis‑regulatory diversity associated with light signaling, development, phytohormone pathways, and stress responses. GO annotation indicated enrichment in terms related to transcription regulator activity, binding, and response to stimulus. Eight salt-responsive genes were selected for RT-qPCR validation, which confirmed their differential expression under salinity. Subcellular localization assays confirmed that HpNAC33 localizes to the nucleus; however, yeast-based transcriptional activation assay did not detect intrinsic transactivation activity for HpNAC33.

CONCLUSION

This study provides a comprehensive genome-wide NAC resource for H. pedunculosum and prioritizes candidate regulators for future dissection of salinity-tolerance mechanisms, while also offering initial insights into the potential mode of action of HpNAC33.