The participation of ABA in the glucose-mediated regulation in Arabidopsis

Abstract

Sugars act as signalling molecules regulating a variety of metabolic and developmental processes in plants. The evidence so far available points that sugar-mediated regulation in plants, occurs through different signalling pathways. To define the components of the sugar signalling pathways, a number of Arabidopsis glucose insensitive (gin) mutants have been isolated. The characterization of such mutants (mainly gin5, gin6) has permitted to propose the participation of the ABA hormone as an essential element of the glucose signalling cascade (Arenas et al.,2000). In agreement, exogenous ABA application restores a normal glucose phenotype in several of our gin mutants. We have also identified a transcriptional factor ABI4, required for proper glucose responses in seedlings. This gene corresponds to an allele of the previously identified ABI4 gene, involved in ABA response (Finkelstein et al., 1998). To understand the role of ABI4 in the glucose-mediated signalling process, we have followed its expression and regulation under different glucose conditions and in different gin mutants. We found that the expression of the ABI4 gene is regulated directly by glucose but not by ABA exogenous application in seedlings. We also showed that transcript level of ABI4 is affected in different of our gin mutants but not in mutants that affect exclusively ABA responses such as abi1, abi2 and abi3. A further physiological and molecular characterization of our gin mutants will also be presented.