IDENTIFICATION OF MUTANTS IN METABOLICALLY REGULATED GENE-EXPRESSION

Sucrose is the main transported form of assimilates, but, significantl y, it also regulates a variety of processes such as photosynthesis and carbon or nitrogen storage. The effects of high sucrose revels are me diated directly by modulation of gene expression. The regulation of st orage protein accumulation, here patatin from potato tubers, was used as a model system to study sucrose mediated signal transduction. The t ranscriptional regulation of patatin genes is conserved in transgenic Arabidopsis, as shown by the analysis of expression of two classes of patatin promoters fused to uidA. Two distinctly different patterns of gene expression were observed. In roots, class I promoter expression i s strongly dependent on the exogenous supply of sugars. 3-O-methylgluc ose induction indicates that the sensor is located upstream of hexokin ase. In contrast, the class II promoter is constitutively active in ro ot tips and hydatodes. The progeny of a homozygous class I line was mu tagenized with ethyl methane sulphonate and screened for signal transd uction mutants using a non-destructive screening system for GUS activi ty. Four mutants showing reduced sucrose responses (rsr) and two mutan ts with modified expression patterns (map) regarding the root tip were identified. In backcross analyses, it was shown that rsr1-1 carries a recessive trans mutation whereas rsr4-1 seems to be a semi-dominant T rans mutation in sugar mediated gene regulation.