Effects of exogenous phytohormones on chlorogenic acid accumulation and pathway-associated gene expressions in sweetpotato stem tips

Abstract

Sweetpotato (Ipomoea batatas [L.] Lam.) stem tips, which contain high concentrations of chlorogenic acid (CGA), are useful as a physiologically functional food to protect against some serious diseases. According to previous studies, exogenous application of phytohormones may be an effective agrotechnical measure to control CGA biosynthesis through the transcriptional regulation of pathway gene expressions. To understand the mechanism of CGA biosynthesis in sweetpotato, we investigated the effects of exogenous phytohormones on CGA metabolism in stem tips of sweetpotato. A significantly elevated CGA content was observed in salicylic acid (SA)-treated sweetpotato stem tips at 72 h, as well as in those subjected to abscisic acid (ABA) or gibberellic acid (GA) treatments. Dynamic expression change of seven enzyme genes involved in sweetpotato CGA biosynthesis were analyzed to determine correlations between transcript levels and CGA accumulation. As revealed by the differential expression of these genes under distinct phytohormone treatments, the regulation of specific pathway genes is a critical determinant of the accumulation of CGA in sweetpotato stem tips. We also found that several hormone-responsive sites, such as those for ABA, GA, SA, and jasmonic acid (JA), were present in the promoter regions of sweetpotato CGA biosynthestic pathway genes. Collectively, phytohormones can regulate the transcription of CGA synthesis-related genes and ultimately affect CGA accumulation in sweetpotato stem tips, whereas the regulatory differences are mirrored by cis-acting elements in the corresponding pathway gene promoters.