Figure 9. A model of JA-mediated high temperature (HT) modulation of flavonoid metabolite biosynthesis.
Under HT (40 ℃), CsHSFA1b and CsHSFA2 are activated and form trimers. Active CsHSFAs promote expression of CsJAZ6 through directly binding to HSE elements in the promoter region of CsJAZ6 . CsJAZ6 can then directly interact with CsEGL3 and CsTTG1, two components of the catechin biosynthetic regulator complex. The CsJAZ6-CsEGL3 interaction interferes with formation of that complex, resulting in repressed catechin accumulation. While spraying tea leaves with MeJA, CsJAZ6 is degraded and released CsEGL3. CsEGL3 can then form the MYB-bHLH-WD40 transcriptional activation complex with CsAN1 and CsTTG1, which directly promotes catechin biosynthesis. CsHSFA and its homologues inArabidopsis negatively regulate JA and anthocyanin accumulation, which regulation is conserved in tea and Arabidopsis.