The latest volume of Journal of Experimental Botany (5 year impact factor=6.538) recently published an article entitled “Transcription factor CitERF71 activates the terpene synthase gene CitTPS16 involved in the synthesis of E-geraniol in sweet orange fruit” (DOI: 10.1093/jxb/erx316). Ph. D student Xiang Li is the first author, Dr. Bo Zhang is the corresponding author. This research is directed by Dr. Kunsong Chen from Zhejiang University and Dr. Harry Klee from University of Florida.
The unique flavor of Citrus fruit depends on complex combinations of soluble sugars, organic acids, and volatile compounds. As economically important fruits, Citrus are rich in volatile terpenoids, monoterpenes are major components of flavor-related volatiles. Among the monoterpenes, E-geraniol is an important volatile, contributing to flavor in sweet orange (Citrus sinensis Osbeck). However, the terpene synthase (TPS) responsible for its synthesis has not been identified in sweet orange, besides, the transcriptional regulation mechanism of related gene is not clear. In the research, we used the C. sinensis genome database, and based on sequence homology and phylogenetic analysis, TPS genes with potential functions in production of volatile monoterpenes were screened out. Terpene synthase 16 (CitTPS16) was shown to catalyze synthesis of E-geraniol in vitro, and transient overexpression of CitTPS16 in fruits and leaves of Newhall sweet orange resulted in E-geraniol accumulation in vivo. Having identified the responsible enzyme, potential transcription regulators of CitTPS16 in the fruit was examined. The real-time qPCR results showed CitERF71 had a similar expression pattern to CitTPS16 during the fruit development, among 48 cloned members of the AP2/ERF transcription factor gene family. Moreover, the activities of these CitERFs with the cloned CitTPS16 promoter were analyzed, CitERF71 was able to activate the CitTPS16 promoter based on results from transient dual-luciferase assays and yeast one-hybrid assays. EMSAs showed that CitERF71 directly binds to ACCCGCC and GGCGGG motifs in the CitTPS16 promoter. These results indicate an important role for CitERF71 in transcriptional regulation of CitTPS16 and, therefore, in controlling production of E-geraniol in Citrus fruit.
This research was supported by the National Key R & D Program of China (2016YFD0400101), the National Natural Science Foundation of China (31672010), and etc.
Article linkage:https://doi.org/10.1093/jxb/erx316
