MUTANTS OF ARABIDOPSIS-THALIANA WITH PLEIOTROPIC EFFECTS ON THE EXPRESSION OF THE GENE FOR BETA-AMYLASE AND ON THE ACCUMULATION OF ANTHOCYANIN THAT ARE INDUCIBLE BY SUGARS

We identified a mutant of Arabidopsis thaliana ecotype Col-0 in which significantly reduced levels of expression of the gene for beta-amylas e (AT beta-Amy) were detected in leaves in response to high concentrat ions of sucrose, glucose or fructose. Genetic studies, including a cro ss with transgenic plants that harbored the AT beta-Amy:GUS transgene with the promoter of AT beta-Amy indicated that this phenotype was cau sed by a recessive mutation, Iba1 that affected expression of AT beta- Amy in trans. We also found a reduced level of sugar-induced expressio n of AT beta-Amy in the Landsberg erecta (Ler) ecotype compared with o ther ecotypes. This phenotype seemed to be due to a recessive trait, p rovisionally designated Iba2, that was linked to neither erecta nor Ib a2. The Iba2 mutation also affected expression of AT beta-Amy:GUS tran sgene. Accumulation of starch and sugars after treatment of leaves wit h sucrose was not affected in the Iba2 mutant and Ler plants. However, both Iba1 mutant and Ler plants accumulated low levels of anthocyanin in response to sucrose, results that suggested the existence of some genetic linkage between regulation of the expression of AT beta-Amy an d regulation of the accumulation of anthocyanin. Although the Iba1 and Iba2 mutations did not affect sugar-inducible gene expression in gene ral, the expression of sugar-regulated genes other than the gene for b eta-amylase was differentially affected in the Iba1 mutant and Ler pla nts. These results suggest that the sugar-regulated expression of many genes in plants might be mediated by multiple signal-transduction pat hways.