The Amplification and Activity Analysis of the Small Rubber Particle Protein (SRPP) Promoter of Eucommia ulmoides (EuSRPP) Revealed That Its Activity Was Regulated by MeJA, GA3, and Drought Pathways

Abstract

As an important temperate gum source plant, Eucommia ulmoides is widely distributed in China, but the low yield of Eucommia ulmoides gum considerably affects its application as a natural rubber in practical production. The small rubber particle protein (SRPP) gene is an influential participant in the Eucommia ulmoides gum biosynthesis process, and its expression affects the gum content. In this study, the promoter activity of the Eucommia ulmoides SRPP (EuSRPP) gene was analyzed by molecular biology and bioinformatics. In order to understand the molecular regulation mechanism of the EuSRPP genes at the transcriptional level, we first obtained the promoter sequences of the EuSRPP1, 3, 4, 5, 6, and 7 genes via genome walking and PCR amplification experiments. Then, the T3 generation of the transgenic homozygous line was obtained via a genetic transformation of Arabidopsis thaliana mediated by Agrobacterium. The six EuSRPP promoters were expressed in transgenic plants and were stably expressed in the leaves, pollinated flowers, and mature pods. As the transgenic plant grows and develops, promoter activity in the root is barely expressed. In addition, after the transgenic Arabidopsis was treated with methyl jasmonate (1 mmol/L MeJA), gibberellin (1 mmol/L GA3), and drought (20% PEG6000), the activity expression of the six EuSRPP promoters increased first and then decreased. The difference, however, is that EuSRPP1, 3, and 4 reach their strongest GUS activity at 3 h of plant treatment, while EuSRPP5, 6, and 7 reach their strongest activity at 6 h of treatment. Based on all experimental results, for the first time, it has been shown that the expression loci of the six EuSRPP gene promoters were relatively consistent. Second, the expression activity of the promoters of the six EuSRPP genes was different under MeJA, GA3, and drought treatment, suggesting that the promoter activity of the EuSRPP genes was regulated by endogenous hormones and drought pathways.