Chilling temperature stimulates growth, gene over-expression and podophyllotoxin biosynthesis in Podophyllum hexandrum Royle

Abstract Podophyllotoxin (PPT) and its derivatives, isolated from the rhizome of Podophyllum hexandrum Royle ( P . hexandrum ), are typically used in clinical settings for anti-cancer and anti-virus treatments. Empirical studies have verified that P . hexandrum had stronger tolerance to chilling, due to involving PPT accumulation in rhizome induced by cold stress. However, the cold-adaptive mechanism and its association with PPT accumulation at a molecular level in P . hexandrum are still limited. In this study, the morpho-physiological traits related to plant growth, PPT accumulation and key gene expressions controlling PPT biosynthesis were assessed by exposing P . hexandrum seedlings to different temperatures (4 °C and 10 °C as chilling stress and 22 °C as the control). The results showed that chilling significantly increased chlorophyll content, net photosynthetic rate, stomatal conductance, and plant biomass, whereas it greatly decreased transpiration rates and intercellular CO 2 concentration. Compared to the control, the chilling treatments under 4 °C and 10 °C conditions induced a 5.00- and 3.33-fold increase in PPT contents, respectively. The mRNA expressions of six key genes were also up-regulated by chilling stresses. The findings are useful in understanding the molecular basis of P . hexandrum response to chilling.