Low-Temperature- and Phosphate Deficiency-Responsive Elements Control DGTT3 Expression in Chlamydomonas reinhardtii

acyl-CoA:Diacylglycerol acyltransferases (DGAT) catalyse the final step of the triacylglycerol biosynthesis. Two major gene families have been shown to encode DGATs, DGAT1, and DGAT2. Abiotic factors such as low temperatures, nitrogen, or phosphorus deficiency was reported to play important roles in the growth and development in green algae. Whether DGATs are induced by low temperatures or phosphorus deficiency, and the corresponding promoter elements are not reported yet. In this study, we found DGTT3 to have a significant response to low temperatures, phosphorus deficiency, and other stresses, such as high concentrations of NaCl, 20 μM GA, and 20 μM abscisic acid. The promoter element of DGTT3 was then studied by deletion and scanning mutagenesis method. Results revealed that the - 319/- 247 region is essential for low-temperature and phosphate-deficiency-mediated induction of DGTT3 expression. The sequence from - 312 to - 299 of the CAATAGACTGCTGCT was the core sequence of the cold responsive element, which facilitated the promoter response to cold induction. Meanwhile, the sequence from - 319 to - 275 was critical to phosphate-deficiency regulation. Furthermore, the relationship between DNA methylation and transgenic silence in -N condition was analyzed, and results showed that the DNA methylation rate of the transformed insertion region was high. This phenomenon was responsible for the decrease in ARS gene expression in the transgenic algal strain under -N conditions.