*2.4. Gene Expression Response to Light and MeJA*

To investigate the effects of light and MeJA on the promoter inducibility at different time points, 

we analyzed *Cppsy* mRNA expression levels after light and MeJA treatment. The results show that on treatment with light, *Cppsy* gene expression increased by up to 36 times, compared with the dark, which indicates that *Cppsy* gene expression is upregulated in response to light (Figure 5A). When treated with MeJA, *Cppsy* gene expression peaked at 10 h after treatment (Figure 5B). Therefore, the gene expression of *Cppsy* is significantly induced by treatment with light and MeJA (*p* < 0.01). These results confirm that the *Cppsy* promoter is induced by light and MeJA, and can be used as a candidate promoter element for the genetic modification of carotenoid biosynthesis in *Chlorella*, other algae, or higher plants. 

**Figure 5.** The expression of *Cppsy* gene induced by light (**A**) and MeJA (**B**) at different time points in *C. protothecoides* CS-41. Data (mean ± SEM) are combined from three independent experiments. # indicates that the gene expression levels were significantly different from that at 0 h (*p* < 0.01). 

## **3. Experimental Section**
