Enhancing health-promoting isothiocyanates in Chinese kale sprouts via manipulating BoESP

Abstract

Glucosinolates (GSLs) are a group of sulfur-containing secondary metabolites, which are abundant in Brassica vegetables. GSL breakdown products (GBPs), especially isothiocyanates (ITCs) benefit human health. Chinese kale is a native Brassica vegetable in China, and its sprouts are rich in GSLs and nutritional substances. ITCs are the predominant GBPs while alternative products are formed in the presence of specifier proteins. However, fewer ITCs are formed in the sprouts. Epithiospecifier (ESP) promotes the formation of epithionitriles at the expense of ITCs in Arabidopsis, but a systematic study of different isoforms of ESPs in most vegetables is still missing. In this study, changes in the content of GBPs and the precursor GSLs, as well as thiols per plant were monitored during sprout development. The proportions of epithionitriles and ITCs in total GBPs were found to be increased and decreased, respectively. RNA-seq showed enhanced expression of numerous genes involved in GSLs biosynthesis and degradation, as well as sulfur assimilation in sprouts compared to seeds. Four copies of BoESPs were isolated and BoESP2 was the most abundant isoform. Generally, transcription of BoESPs showed a strong response to abscisic acid and gibberellin, and consequently epithionitriles increased under these treatments. Knockdown of BoESP2 expression through virus-induced gene silencing system could effectively increase total ITCs and decrease total epithionitriles. Overall, dynamic GSL metabolic flux exists in the sprouting period, and the expression of BoESPs determines the pattern of GBPs, suggesting that improving the health-promoting ITCs in Chinese kale sprouts through manipulating BoESPs by metabolic engineering is feasible.

Acknowledgements

We are grateful to Prof. Mingfang Zhang (Zhengjiang University, China) for kindly providing the plasmid pTY-S. This work was supported by National Natural Science Foundation of China (32172593), Natural Science Foundation of Zhejiang Province (LY21C020002), Science and Technology Plan Project of Ningbo City (2021Z132), and Zhejiang Province Commonweal Projects (NOLGN20C150009).

Author contributions

Q.W. and H.M. conceived and designed the research. H.M., C.X., S.Y., J.W. and Y.Z. performed the experiments and analysed the data. H.M., C.X., and Q.W. wrote the manuscript. All authors read and approved the manuscript.

Data availability

The datasets that support the findings of this study are available from the corresponding author upon reasonable request.

Conflict of interest

The authors declare that they have no conflict of interest.

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