Roles of JA in regulating catechin biosynthesis under HT
It has been demonstrated that JA plays an important role in the regulation of flavonoid biosynthesis, including proanthocyanidins and anthocyanins (An et al., 2015). When tea plants were exposed to HT, we noticed that JA-responsive genes including CsLOX1 , CsAOS , and CsMYC2 were down-regulated, suggesting impaired JA signaling to be associated with HT exposure (Figure 3a). Given the lower content of MeJA in HT-treated tea leaves (Figure 3b), we wondered whether the JA pathway mediates the inhibiting effect of HT on catechin biosynthesis. After spraying tea leaves with MeJA, ibuprofen (a JA synthesis inhibitor), and MeJA plus MG132, we then transferred pre-treated plants into growth chambers to grow at 25 ℃ or 40 ℃ for 3 d. Subsequent HPLC analysis revealed that HT significantly reduced catechin content with an average reduction of 15.5%, and ibuprofen treatment also repressed catechin accumulation by 32.8%, whereas treatment with MeJA alleviated the inhibitory effect of HT on catechin biosynthesis, resulting in catechin levels about equal to those in plants grown at normal temperature (Figure 3c). Consistent with the observed changes in catechin levels, expression of biosynthetic genes includingCsCHS , CsDFR , and CsANS was significantly inhibited in plants sprayed with ibuprofen and the expression patterns resembled those in plants treated with HT, whereas MeJA was able to partly counteract the inhibition caused by HT (Figure 3d).