Comparative analysis of the NAC gene family in five Polygonaceae species, focusing on Rheum officinale Baill

BACKGROUND: Transcription factors (TFs), particularly the plant-specific NAC family, act as master regulators of growth, development, and stress responses. While NAC genes have been characterized in many plant lineages, comprehensive knowledge within the Polygonaceae family remained limited. RESULTS: This study systematically identified and characterized the NAC gene family in five Polygonaceae species: R. officinale, R. tanguticum, R. nobile, F. multiflora, and F. tataricum. Across these species, 481 NAC genes were identified, with counts ranging from 80 in F. tataricum to 106 in R. officinale. Phylogenetic analysis clustered these genes into nine clades. Segmental duplication was the primary driver of NAC family expansion across all species. Collinearity analysis revealed 47 orthologous gene pairs across the five species. In R. officinale, gene structure and motif analysis revealed conserved domains and diverse cis-regulatory elements associated with hormone signaling, stress responses, and development. Transcriptome and RT-qPCR analyses confirmed that numerous R. officinale NAC genes (RoNACs) are dynamically regulated by hormone treatments (MeJA, ABA, SA, Eth) and abiotic stresses (salt, drought, cold, heat, UV-B). Notably, HPLC analysis showed UV-B irradiation markedly changed the levels of anthraquinone secondary metabolites in R. officinale leaves. RoNAC88 and RoNAC105 emerged as key regulators of UV-B responses in R. officinale. RoNAC88 was consistently upregulated under cold, heat, and UV-B stresses. In contrast, RoNAC105 showed stress-specific expression patterns: downregulated under drought, but upregulated under cold and UV-B. Collectively, these findings highlight RoNAC88 and RoNAC105 as valuable genetic resources for enhancing stress tolerance in R. officinale. CONCLUSIONS: This study identified RoNAC88 and RoNAC105 as valuable genetic resources for enhancing stress tolerance in R. officinale.