CIS-ACTING ELEMENTS OF THE CHS1 GENE FROM WHITE MUSTARD CONTROLLING PROMOTER ACTIVITY AND SPATIAL PATTERNS OF EXPRESSION

Chalcone synthase (CHS) catalyses the first regulatory step in the bra nch pathway of phenylpropanoid biosynthesis specific for synthesis of ubiquitous flavonoid pigments and UV protectants. External stimuli suc h as stress, light and wounding induce CHS expression that is both tis sue-specific and under developmental control. In order to identify cis -acting elements involved in organ and tissue specifity, we fused vary ing parts of the CHS1 promoter of white mustard (Sinapis alba L.) to t he GUS-coding region and analysed the expression of these constructs i n stably transformed Arabidopsis plants. Two different stages of devel opment were examined, seedlings as an early stage and flowers as the f inal stage of development. In seedlings, the full-length promoter show ed expression in all organs except the hypocotyl: in flowers expressio n could be observed in all whorls. Unit 1 of the mustard CHS1 promoter , an element conserved in several CHS genes, which has been recently i dentified as a light responsive element, is able to mediate a tissue-s pecific expression pattern similar to that obtained with the full-leng th promoter in seedlings as well as in flowers. Ether elements enhance or repress expression in combination with Unit 1, or mediate defined spatial expression independently of Unit 1. One such element, located between -907 and -655, directs expression similar to that of the full- length promoter in flowers but not in seedlings and differs therefore in function to Unit 1. Our data suggest a dominant regulation of CHS1 expression by Unit 1. Ether elements within this promoter might intera ct with Unit 1 or confer a subset of spatial expression patterns when Unit 1 is deleted.