Comparative iTRAQ-based proteomic analysis provides insight into a complex regulatory network of Pogostemon cablin in response to exogenous MeJA and Ethrel

Exogenous hormone application is an effective and feasible method to regulate production of economic plant and synthesis of high-value natural medical products. Jasmonate and ethylene are two crucial plant hormones regulate growth and development, secondary metabolism, and stress responses in Pogostemon cablin. However, the regulatory mechanism of these phytohormones in this important medicinal plant has not been elucidated to date. In the present study, alterations of secondary metabolites and photosynthesis of P. cablin leaves treated with exogenous methyl jasmonate (MeJA), ethrel (ETH), and simultaneously with both MeJA and ETH, respectively, were explored. To uncover the potential protein functional network involved in the hormone-induction mechanism, we performed a proteomic analysis of differently treated leaves using isobaric tags for relative and absolute quantification (iTRAQ). In P. cablin leaves before and after three different treatments, 254, 229 and 400 differentially expressed proteins (DEPs) involving a wide range of physiological processes were clearly identified respectively. The quantitative data were further validated by parallel reaction monitoring (PRM) and qRT-PCR. Functional enrichment analysis indicated photosynthesis-related proteins showed a significant increase expression in P. cablin leaves after MeJA treatment, while proteins involved in secondary metabolite biosynthesis and thiamine metabolism were significantly down-regulated. Exogenous ETH mainly repressed the expression of proteins related to carbohydrate and energy metabolism in P. cablin leaves while markedly raised protein abundance in photosynthesis and protein processing in the endoplasmic reticulum. Regarding P. cablin leaves treated with both MeJA and ETH, expression of proteins related to carbohydrate and energy metabolism, secondary metabolite biosynthesis, tyrosine metabolism, thiamine metabolism and lipid metabolism were significantly down-regulated, while that of proteins involved in photosynthesis, phenylpropanoid biosynthesis and nitrogen metabolism were considerably up-regulated. This is the first study using iTRAQ-based proteomics approach to comprehensively elucidate exogenous hormone response of P. cablin, providing important pathways/proteins involved in secondary metabolism regulation, which will contribute to potential genetic improvement of medical constituents.