The CaMV-35S promoter is sensitive to shortened photoperiod in transgenic tobacco

The CaMV-35S promoter is one the most widely used promoters in transgenic plant research because it exhibits a high level of transcriptional activity in a variety of plant tissues. Here, the CaMV-35S promoter fused to the GUS gene was used as a model for constitutive expression in transgenic Nicotiana tabacum (cv 'Xanthi') leaves. The transgenic plants were placed under a shortened photoperiod to determine if GUS expression changed; measurements were made using fluorometry and ribonuclease protection assays. When the plants were moved from a 16 : 8-h photoperiod to a 8 : 16-h photoperiod, an increase in both specific GUS activity and gus RNA levels was observed, and these levels decreased upon returning to the 16 : 8-h photoperiod. These results indicate that photoperiod plays an important role in the regulation of the CaMV-35S promoter. Studies involving a comparison of this promoter to others should be limited to constant photoperiod conditions.