SmGRAS5 regulates GA-promoted biosynthesis of tanshinones
Since SmGRAS5 OE lines grow slower than the control, which was
similar to the GA-deficient phenotypes (Fig. S4). Consistent with the
phenotypes, overexpression of SmGRAS5 indeed decreased the GA
content and downregulated the expressions of most GA biosynthetic genes
(Fig. 4A,C). To further investigate whether the regulatory function of
SmGRAS5 on tanshinones biosynthesis is mediated by GA, we then used
exogenous GA to treat the SmGRAS5 OE and control lines. We found
that there are some GA-responded motifs (GARE-motif and P-box) in the
promoter of SmGRAS5. And we also found GA treatment could induce the
expression of SmGRAS5 (Fig. S5). The results showed that the GA
content of control and SmGRAS5 OE lines were all significantly
increased after GA treated. However, the expressions of the downstream
genes of GA biosynthesis were different in the SmGRAS5 OE lines.
GA biosynthetic enzymes SmGA20ox2/6 were upregulated, whileSmGA3ox1 was downregulated in the SmGRAS5 OE lines. And
the expressions of the GA deactivating enzymes SmGA2ox8/9 were
different in the SmGRAS5 OE lines. The results after GA treatment
indicated that the increased GA content in the SmGRAS5 OE lines
maybe not have occurred by promoting GA biosynthesis but could have also
been caused by exogenous GA entering the cell. Intriguingly, the four
tanshinones total contents of SmGRAS5 OE and control lines were
all significantly increased under GA treatments (Fig. 4B). As expected,
the expression of most
tanshinones
biosynthesis genes was quickly induced by GA application in all the
lines (Fig. 4C). Among the tanshinones biosynthesis genes, the
downstream genes GGPPS1 and KSL1 had the most
significantly increased in the SmGRAS5 OE and control lines.
Collectively, these results indicated that GA could induceSmGRAS5 response to further promote tanshinone biosynthesis.