Unit 1 of the mustard chalcone synthase promoter is sufficient to mediate light responses from different photoreceptors

Abstract

Chalcone synthase (CHS) expression in mustard is light regulated and depends on the action of different photoreceptors (i.e. phytochrome, blue 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 on which sequences mediate the light response and which photoreceptors are involved. With transient expression studies with parsley protoplasts, we have identified a single light-responsive element (LRE) within the mustard chs promoter with high similarity to Unit 1, one of two LREs 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 cauliflower 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, our studies indicate different in vitro binding to proteins from parsley cells. We conclude that the activation of different chs genes may occur by the use of different DNA-binding activities.