UNIT-1 OF THE MUSTARD CHALCONE SYNTHASE PROMOTER IS SUFFICIENT TO MEDIATE LIGHT RESPONSES FROM DIFFERENT PHOTORECEPTORS

Chalcone synthase (CHS) expression in mustard is light regulated and d epends on the action of different photoreceptors (i.e. phytochrome, bl ue and UV-light photoreceptors). It has been shown previously 1 that approximately 1 kbp of the promoter of the chs1 gene from mustard 2 is sufficient for light-induced expression. In this paper, we focus o n which sequences mediate the light response and which photoreceptors are involved. With transient expression studies with parsley protoplas ts, we have identified a single light-responsive element (LRE) within the mustard chs promoter with high similarity to Unit 1, one of two LR Es of the parsley chs gene 3. We have also demonstrated that Unit 1 of the mustard chs gene, when fused to the minimal 35S promoter from c auliflower mosaic virus (CaMV), responds to different photoreceptors ( UV, blue, phytochrome), a response indistinguishable from that of the full-length promoter. Unit 1 therefore is sufficient to mediate light responses from three photoreceptors. Although Unit 1 from mustard and parsley chs genes show striking similarity in sequence and function, o ur studies indicate different in vitro binding to proteins from parsle y cells. We conclude that the activation of different chs genes may oc cur by the use of different DNA-binding activities.