Heat Shock Transcription Factor HSF2b Plays a Critical Role in the Synthesis of Fucoxanthin by Modulating the Expression of ZEP1 in Phaeodactylum tricornutum

Fucoxanthin is a pigment with important economic value, however, the transcriptional regulatory mechanism of its synthetic pathway is relatively poorly reported. In this study, we screened a heat-excited transcription factor, HSF2b, which is able to bind to the ZEP1 promoter, using a yeast one-hybrid screen library. Functional studies revealed that overexpression of HSF2b increased the content of fucoxanthin, while gene editing of HSF2b decreased the content of fucoxanthin. Further studies showed that HSF2b was able to further mediate the synthesis of fucoxanthin by regulating the expression of the fucoxanthin synthesis-related genes DXS, PSY1, ZDS, ZEP1, ZEP3 and CRTISO5. In addition, HSF2b was able to bind to the promoters of ZEP1, ZEP3 and CRTISO5 and activate their expression. The results of genetic studies showed that the regulation of fucoxanthin by HSF2b was dependent on ZEP1. Therefore, the present study systematically elucidated the transcriptional regulatory mechanism of fucoxanthin synthesis, which provides a new idea for understanding the mechanism of fucoxanthin synthesis.