Integrated physiological and transcriptomic analysis reveals mechanism of leaf in Phellodendron Chinense Schneid seedlings response to drought stress

Phellodendron chinense Schneid (P. chinense Schneid) is a traditional Chinese woody medicinal plant which contains berberine, phellodendrine and other bioactive compounds, and has an important function on anti-tumor, anti-inflammation, bacteriostasis, reducing blood sugar and fat. The growth and alkaloid biosynthesis of P. chinense Schneid are affected by drought stress, while influence the yield and quality. However, the mo-lecular mechanism of P. chinense Schneid seedlings response to drought stress at transcriptional and physiological levels are not clear. In this study, physiological and transcriptomic responses of P. chinense Schneid seedling leaf to drought stress were investigated. The P. chinense Schneid seedlings were irrigated to field capacity (NC), 40% field capacity (moderate drought, MD) and 20% field capacity (severe drought, SD). The results showed that MD and SD treatments promoted ROS generation, reduced Chl contents and photosynthetic efficiencies, inhibited shoot growth, but increased phellodendrine contents in leaves compared to the NC treatments. A total of 54325 unigenes were identified in MD and SD treatment samples, and the differentially expressed genes (DEGs) were primarily involved in several pathways of photosynthesis, phytohormone biosynthesis and signal transduction and isoquiholine alkaloid biosynthesis, with the ethylene (ET) signaling pathway especially. Moreover, some transcription factors from DEGs were revealed, which chiefly related to ET signal transduction, leaf development and alkaloid biosynthesis. Our study suggested that the P. chinense Schneid seedlings responded to drought stress mainly through ET signaling pathway.