Characteristics of chalcone synthase promoters from different leaf-color malus crabapple cultivars

Abstract

Anthocyanins are secondary metabolites of higher plants that contribute to the colors of leaves and flowers, and chalcone synthase is the first key enzyme in anthocyanin biosynthesis. We isolated a 2.4-kb and a 1.8-kb 5′-upstream sequence of chalcone synthase (McCHS) from ‘ever-green-leaf’ and ‘ever-red-leaf’ color types of Malus crabapple cvs. ‘Flame’ and ‘Royalty’, respectively, and found a 743-bp fragment missing from ‘Flame’ when comparing these sequences. The missing sequence contained two MYBPLANT elements and three MYBCORE elements that are essential for MYB transcription-factor binding and inducing anthocyanin biosynthesis. Thus, we concluded that the lack of these important cis-elements was a reason for the low expression level of McCHS in ‘Flame’. GUS activity and transient expression assays showed a series of 12 deletion promoter fragments had promoter activity and could drive GUS expression; however, the GUS staining color and the GUS activity were different, indicating that different fragments had different promoter activity. Tissue expression assays in stable transgenic tobacco showed that the McCHS promoter was expressed widely, i.e. in leaves, roots and stems. To sum up, the McCHS promoter has potential application in genetic transformation to improve plant color.