Analysis of the spatial and temporal expression pattern directed by the Populus tomentosa 4-coumarate:CoA ligase Pto4CL2 promoter in transgenic tobacco.

4-Coumarate:CoA ligase (4CL) is a key enzyme in the phenylpropanoid synthesis pathway. The Pto4CL2 promoter was cloned from Populus tomentosa Carr. and fused to the reporter gene encoding β-glucuronidase (GUS); the complex expression patterns directed by the Pto4CL2 promoter were then characterized in Nicotiana tabacum Xanthi by histochemical assays. The promoter 5'-deletion and histochemical assay conducted on transformants indicated that the -317 to -292 nt region supports Pto4CL2 expression in the epidermis and petals and the deletion of the -266 to -252 nt region resulted in the loss of tissue specificity and a dramatic reduction in GUS activity. Furthermore, electrophoretic mobility shift assays testified that an adenine and cytosine-rich element (-264 to -255 nt) and an abscisic acid-responsive element (-242 to -235 nt) in the Pto4CL2 promoter would have functions for the complex expression profiling and efficient basal expression, respectively. These results further clarify the mode of the regulatory expression of class II 4CL promoters in higher plants.