The interaction between transcription factors and cis-acting regulatory sequences presented in plant promoters is a key step involved in the regulation of plant gene expression. As a result, much effort has been made to dissect various plant promoters, to identify different transcription factors, and to study their specific interactions. Commonly, in vivo characterization of plant promoters and transcription factors is carried out by generation and analysis of transgenic plants expressing promoter/reporter gene fusion and/or corresponding trans-factors. This process is labor-intensive, time-consuming, and usually takes several months. In addition, transgene expression in transgenic plants often varies significantly due to insert position and other effects, thus complicating data analysis. To overcome some of those disadvantages, methods for transient expression analysis have been developed as convenient alternatives to stable transformation (该短文引自：The Plant Journal, 26: 543).
