An endogenous promoter discovered in duckweed: a promising transgenic tool for plants.

Promoters are one of the most critical elements in regulating gene expression. They are considered essential biotechnological tools for heterologous protein production. The one most widely used in plants is the promoter from . However, our study for the first time discovered the promoter reduced the expression of exogenous proteins under increased antibiotic stress. We discovered an endogenous strong promoter from duckweed named that keeps higher initiation activity under antibiotic stress. Stable transformation in duckweed showed that the gene expression of in the was 1.76 times that of the at 100 mg.L G418 and 6.18 times at 500 mg.L G418. Notably, with the increase of G418 concentration, the gene expression and the fluorescence signal of in the were weakened, while the only changed slightly. This is because, under high antibiotic stress, the promoter was methylated, leading to the gene silencing of the gene. Meanwhile, the promoter was not methylated and maintained high activity. This is a previously unknown mechanism that provides us with new insights into screening more stable promoters that are less affected by environmental stress. These outcomes suggest that the promoter has a high capacity to initiate the expression of exogenous proteins. In conclusion, our study provides a promoter tool with potential application for plant genetic engineering and also provides new insights into screening promoters.