Multiple Roles of AIP6 in Developmental Regulation of Arabidopsis

Genetic studies have implicated the abscisic acid (ABA) transducing factors ABI3, ABI4 and ABI5, in responses to high sugar-induced stress and ABA. Although ABI3 mRNA and protein expression are confined mainly to late embryogenesis, analyses of abi3 mutants indicate the gene functions also during vegetative development. Using the yeast two-hybrid system we identified ABI3 Interacting Protein 6 (AIP6, At3g05545) as a possible regulator of ABI3 function. AIP6 is a RING-type, E3 ubiquitin protein ligase with demonstrated E3 activity in vitro. Our lab has shown that epitope-tagged, full-length AIP6 and ABI3 form a complex in vivo, in yeast and in planta (L. Host et al, 2007). In order to define the function of AIP6 in planta, homozygous aip6 mutant alleles (T DNA insertion) were characterized. Homozygous aip6 alleles show an increase in seed dormancy and sensitivity to inhibition of germination by ABA, delayed flowering time under short day conditions but not under long day conditions, and an increase in ABI3 protein levels when compared to the wild-type (Col-O) control. All these traits are consistent with enhanced activity of ABI3 and possibly an ABI3-related factor, indicative of a role for AIP6 as a negative regulator of ABI3. Massively Parallel Signature Sequencing (MPSS) and Tilling array demonstrates that AIP6 is expressed ubiquitously in Arabidopsis suggesting multiple targets and possibly multiple roles during plant development