Abstract: The objective of this study was to establish an efficient transient transformation system for the corollas of Tagetes erecta and to investigate the promoter activity of TeCYC2c, a key gene regulating floral organ symmetry. A fusion expression vector, incorporating the CaMV 35S promoter and the GUS reporter gene, was constructed to facilitate the transient transformation in Tagetes erecta corollas. The study delved into the effects of bacterial strain type, bacterial suspension concentration, infection time, and co-culture time on the transient transformation efficiency of the GUS gene. The results revealed that the GV3101 strain achieved the highest infection efficiency. The bacterial suspension concentration, quantified at an OD₆₀₀ value of 1.0, yielded the most robust transformation efficiency. The infection time was observed to exert no substantial influence on transient transformation efficacy. Moreover, a co-culture time of 24 hours was identified as the optimal condition for the process. Based on this transient transformation system for the Tagetes erecta corollas, the promoter activity of the TeCYC2c gene was investigated. A 1 735 bp upstream sequence of the TeCYC2c gene was cloned and four promoter deletion expression vectors, with the GUS gene as the reporter gene, were constructed based on the distribution and quantity of elements predicted by PlantCARE. Subsequently, these vectors were employed for transiently transformation of Tagetes erecta corollas to facilitate an in-depth analysis of promoter activity. The results revealed that the core region of the promoter was located at –650 to –1 bp. It was speculated that the light-responsive elements within this region positively upregulated the expression of downstream genes, while the hormone-responsive and stress-responsive elements unique to pTeCYC2c(-1735) and pTeCYC2c(-1406) might have an inhibitory effect on promoter-driven downstream gene expression. By combining the establishment of the transient transformation system for the marigold corollas and the promoter activity analysis of TeCYC2c gene, a technical foundation has been laid for further rapid elucidation of the functions of genes related to floral organ development.

Key words: Tagetes erecta, TeCYC2c, promoter, transient expression, GUS activity