Distinct cis-acting elements direct the germination and sugar responses of the cucumber malate synthase gene

The malate synthase gene (ms) promoter in cucumber (Cucumis sativus L.) was investigated with the aim of distinguishing DNA sequences mediating regulation of gene expression by sugar, and expression following seed germination. Promoter deletions were constructed and their ability to direct expression of the beta-glucuronidase (gus) reporter gene was investigated in transgenic Nicotiana plumbaginifolia. Gene expression was assayed in germinating seeds and developing seedlings (the germination response) and in seedlings transferred from light into darkness with and without sucrose (the sugar response). As progressively more of the promoter was deleted from the 5' end, first the sugar response and then the germination response was lost. Thus, distinct regions of the promoter are required for carbohydrate control and for regulation of gene expression in response to germination. Sequence comparisons of the ms promoter with that of the isocitrate lyase gene (icl) of cucumber have previously identified four IMH (ICL-MS Homology) sequences. One such sequence, IMH2, is shown here to be implicated in the sugar response of the ms gene. The 17 bp sequence, which when deleted from the ms gene results in loss of the germination response, contains a 14 bp sequence which is similar to a sequence in the icl promoter, which we refer to as IMH5. Furthermore, this sequence has similarity with amdI9-like sequences in filamentous fungi, which confer facB-mediated acetate inducibility on several genes, including those encoding ICL and MS.