EuTGA1, a bZIP transcription factor, positively regulates EuFPS1 expression in Eucommia ulmoides

Eucommia ulmoides (E. ulmoides) is widely cultivated and exhibits remarkable adaptability in China. It is the most promising rubber source plant in the temperate zone. E. ulmoides gum (EUG) is a trans-polyisoprene with a unique "rubber-plastic duality", and is widely used in advanced materials and biomedical fields. The transcription of Farnesyl pyrophosphate synthase (FPS), the rate-limiting enzyme of EUG biosynthesis, is controlled by regulatory mechanisms that remain poorly elucidated. In this research, 12 TGA transcription factors (TFs) in E. ulmoides were identified. Promoter prediction results revealed that the EuFPS1 promoter had binding sites for EuTGAs. Subsequently, the EuTGA1 was obtained by screening the E. ulmoides cDNA library using the EuFPS1 promoter as a bait. The individual yeast one‑hybrid and dual-luciferase assays confirmed that in the tobacco plant, EuTGA1 interacted with the EuFPS1 promoter, resulting in a more than threefold increase in the activity of the EuFPS1. Subcellular localization study further revealed that EuTGA1 is localized in the nucleus and acts as a TF to regulate EuFPS1 expression. In addition, qRT-PCR analysis demonstrated that the expression trend of EuFPS1 and EuTGA1 was the same at different time of the year. Notably, low temperature and MeJA treatments down-regulated EuTGA1 expression. Additionally, the transient transformation of EuTGA1 enhanced NtFPS1 expression in tobacco plants. Overall, this study identified a TF that interacted with EuFPS1 promoter to positively regulate EuFPS1 expression. The findings of this study provide a theoretical basis for further research on the expression regulation of EuFPS1.

Positive regulation of the Eucommia rubber biosynthesis-related gene EuFPS1 by EuWRKY30 in Eucommia ulmoides

Eucommia rubber is a secondary metabolite from Eucommia ulmoides that has attracted much attention because of its unique properties and enormous potential for application. However, the transcriptional mechanism regulating its biosynthesis has not yet been determined. Farnesyl pyrophosphate synthase is a key enzyme in the Eucommia rubber biosynthesis. In this study, the promoter of EuFPS1 was used as bait, EuWRKY30 was screened from the cDNA library of EuFPS1 via a yeast one-hybrid system. EuWRKY30 belongs to the WRKY IIa subfamily and contains a WRKY domain and a C2H2 zinc finger motif, and the expressed protein is located in the nucleus. EuWRKY30 and EuFPS1 exhibited similar tissue expression patterns, and yeast one-hybrid and dual-luciferase experiments confirmed that EuWRKY30 directly binds to the W-box element in the EuFPS1 promoter and activates its expression. Moreover, the overexpression of EuWRKY30 significantly upregulated the expression level of EuFPS1, further increasing the density of the rubber particles and Eucommia rubber content. The results of this study indicated that EuWRKY30 positively regulates EuFPS1, which plays a critical role in the synthesis of Eucommia rubber, provided a basis for further analysis of the underlying transcriptional regulatory mechanisms.