Differential expression of three ABA-insensitive five binding protein (AFP)-like genes in wheat.

Abscisic acid (ABA) signaling includes positive and negative regulators in the signaling pathway. ABA-insensitive five (ABI5) binding protein (AtAFP), one of the negative regulators found in Arabidopsis, is involved in the proteolysis of a positive regulator, ABI5 (bZIP-type transcription factor). Three wheat orthologs (TaAFPs) of AtAFP were isolated. TaAFPs have a nuclear localization domain in the middle of the deduced amino acid sequence and an ABI5 binding domain in the C-terminal region as AtAFP. Three TaAFPs were located on the short arms of chromosomes 2A, 2B, and 2D of wheat, and based on their chromosomal locations, they were named TaAFP-A, TaAFP-B, and TaAFP-D. In comparison to AtAFP, which was activated in developing seeds and the early stage of germination, TaAFPs were expressed in a greater variety of tissues, such as flag leaves, roots, and leaves of seedlings, and developing grains. TaAFP-B was expressed predominantly in all tissues examined; TaAFP-A and TaAFP-D responded to ABA and stresses, such as salt and dehydration. These three TaAFPs may differentiate their roles in ABA signaling during wheat evolution.