Genome-wide analysis of ARF transcription factors reveals HcARF5 expression profile associated with the biosynthesis of β-ocimene synthase in Hedychium coronarium.

Herein, 37 ARF genes were identified and analyzed in Hedychium coronarium and HcARF5 showed a potential role in the regulation of HcTPS3. Auxin is an important plant hormone, implicated in various aspects of plant growth and development processes especially in the biosynthesis of various secondary metabolites. Auxin response factors (ARF) belong to the transcription factors (TFs) gene family and play a crucial role in transcriptional activation/repression of auxin-responsive genes by directly binding to their promoter region. Nevertheless, whether ARF genes are involved in the regulatory mechanism of volatile compounds in flowering plants is largely unknown. β-ocimene is a key floral volatile compound synthesized by terpene synthase 3 (HcTPS3) in Hedychium coronarium. A comprehensive analysis of H. coronarium genome reveals 37 candidate ARF genes in the whole genome. Tissue-specific expression patterns of HcARFs family members were assessed using available transcriptome data. Among them, HcARF5 showed a higher expression level in flowers, and significantly correlated with the key structural β-ocimene synthesis gene (HcTPS3). Furthermore, transcript levels of both genes were associated with the flower development. Under hormone treatments, the response of HcARF5 and HcTPS3, and the emission level of β-ocimene contents were evaluated. Subcellular and transcriptional activity assay showed that HcARF5 localizes to the nucleus and possesses transcriptional activity. Yeast one-hybrid (Y1H) and dual-luciferase assays revealed that HcARF5 directly regulates the transcriptional activity of HcTPS3. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays showed that HcARF5 interacts with scent-related HcIAA4, HcIAA6, and HcMYB1 in vivo. Overall, these results indicate that HcARF5 is potentially involved in the regulation of β-ocimene synthesis in H. coronarium.