Selecting transformed plants is generally time consuming and laborious. To develop a method for transgenic plant selection without the need for antibiotics or herbicides, we evaluated the suitability of the R2R3 MYB transcription factor gene CaAN2 from purple chili pepper (Capsicum annuum) for use as a visible selection marker. CaAN2 positively regulates anthocyanin biosynthesis. Transient expression assays in tobacco (Nicotiana tabacum) leaves revealed that CaAN2 actively induced sufficient pigment accumulation for easy detection without the need for a basic helix-loop-helix (bHLH) protein as a cofactor; similar results were obtained for tobacco leaves transiently co-expressing the anthocyanin biosynthesis regulators bHLH B-Peru from maize and R2R3 MYB mPAP1D from Arabidopsis. Tobacco plants harboring CaAN2 were readily selected based on their red color at the shoot regeneration stage due to anthocyanin accumulation without the need to impose selective pressure from herbicides. Transgenic tobacco plants harboring CaAN2 showed strong pigment accumulation throughout the plant body. The ectopic expression of CaAN2 dramatically promoted the transcription of anthocyanin biosynthetic genes as well as regulators of this process. The red coloration of tobacco plants harboring CaAN2 was stably transferred to the next generation. Therefore, anthocyanin accumulation due to CaAN2 expression is a useful visible trait for stable transformation, representing an excellent alternative selection system for transgenic plants.
Keywords: CaAN2; Capsicum annuum; alternative selection method; anthocyanin; transformation; visible marker.