HT inhibits flavonoid biosynthesis in tea leaves
HT is known to influence secondary metabolism in various plant species. To explore its effect and associated regulation mechanism in tea, we compared the metabolites from tea leaves grown under normal (25 ℃) and HT (40 ℃) conditions. The results showed that 58 metabolites were up-regulated and 53 down-regulated in HT conditions (Figure 1a). It is worth noting that 11 of the 15 detected flavonoids were significantly decreased, including catechin which are featured compounds in tea. HPLC analysis further confirmed that leaves from tea plants exposed to HT accumulate less catechin than those grown in normal conditions (Figure 1b).
Next, we examined the expression levels of catechin biosynthetic genes through qRT-PCR. Consistent with the changes in metabolic products, the transcript levels of genes encoding pertinent enzymes includingCsPAL (TEA023243.1 ), CsCHS (TEA023340.1 ),CsCHI (TEA034003.1 ), CsF3H (TEA023790.1 ),CsF3’H (TEA006847.1) , CsDFR (TEA022775.1 ),CsFLS (TEA033416.1) and CsANS (TEA015769.1 ) were lower in tea leaves treated with HT than those grown under normal conditions (Figure 1c). The qRT-PCR results also showed that eight of the 25 CsHSFs identified in tea were responsive to HT in different degrees (Figure 1d). Among those, CsHSFA1a andCsHSFA2 exhibited especially altered expression, climbing up to more than 50-fold above normal (Figure 1d).