Identification and characterization of PcHD8 from Pogostemon cablin related to the regulation of trichome development

Pogostemon cablin, a herbaceous plant of the Lamiaceae family, is widely recognized for the medicinal and industrial applications of its dried aerial parts. The plant's surface is densely populated with trichomes, which are believed to be the primary sites for the biosynthesis and accumulation of patchouli essential oil. However, the molecular mechanisms underlying the development of these trichomes in P. cablin remain largely unexplored. This study employed transcriptomic sequencing to identify and characterize genes co-regulated in trichome development and essential oil biosynthesis in P. cablin. Notably, we report the first identification of PcHD8, a member of the HD-ZIP gene family. Homologous genes, such as AaHD8 in Artemisia annua and SlHD8 in Solanum lycopersicum, have been shown to promote both trichome formation and secondary metabolite synthesis. We cloned PcHD8 and overexpressed it in Nicotiana tabacum, which resulted in a significant increase in trichome density compared to the control. Conversely, silencing PcHD8 via virus-induced gene silencing (VIGS) in P. cablin led to a marked reduction in trichome density. GC-MS analysis revealed a significant decline in the key biomarkers of patchouli essential oil, patchouli alcohol and pogostone, following PcHD8 silencing. These findings establish PcHD8 as a key positive regulator of trichome development and essential oil biosynthesis. This study offers critical insights into the genetic regulation of plant traits affecting medicinal quality. Our findings highlight PcHD8 as a promising candidate gene for molecular breeding in P. cablin and may provide a reference for research on other trichome-rich, volatile oil-producing plants.