Direct targets of the transcription factors ABA-Insensitive(ABI)4 and ABI5 reveal synergistic action by ABI4 and several bZIP ABA response factors

• Published in: Plant molecular biology 2011-03, Vol.75 (4-5), p.347-363
• Main Authors: Reeves, Wendy M., Lynch, Tim J., Mobin, Raisa, Finkelstein, Ruth R.
• Format: Article
• Language: English
• Subjects: Abscisic acid; Abscisic Acid - metabolism; Abscisic Acid - pharmacology; Arabidopsis - drug effects; Arabidopsis - genetics; Arabidopsis - growth & development; Arabidopsis - metabolism; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Base Sequence; Basic-Leucine Zipper Transcription Factors - genetics; Basic-Leucine Zipper Transcription Factors - metabolism; Binding Sites - genetics; Bioassays; Biochemistry; Biomedical and Life Sciences; DNA Primers - genetics; DNA, Plant - genetics; DNA, Plant - metabolism; Gene expression; Gene Expression Regulation, Developmental - drug effects; Gene Expression Regulation, Plant - drug effects; Genes, Plant; Germination; Hormones; Life Sciences; Molecular biology; Mutation; Plant biology; Plant Growth Regulators - metabolism; Plant Growth Regulators - pharmacology; Plant Pathology; Plant Sciences; Plants, Genetically Modified; Promoter Regions, Genetic; Seed germination; Seedlings; Seeds; Seeds - drug effects; Seeds - growth & development; Seeds - metabolism; Transcription Factors - genetics; Transcription Factors - metabolism; Two-Hybrid System Techniques; Yeasts
• ISSN: 0167-4412; 1573-5028
• DOI: 10.1007/s11103-011-9733-9

The plant hormone abscisic acid (ABA) is a key regulator of seed development. In addition to promoting seed maturation, ABA inhibits seed germination and seedling growth. Many components involved in ABA response have been identified, including the transcription factors ABA insensitive (ABI)4 and ABI5. The genes encoding these factors are expressed predominantly in developing and mature seeds, and are positive regulators of ABA mediated inhibition of seed germination and growth. The direct effects of ABI4 and ABI5 in ABA response remain largely undefined. To address this question, plants over-expressing ABI4 or ABI5 were used to allow identification of direct transcriptional targets. Ectopically expressed ABI4 and ABI5 conferred ABA-dependent induction of slightly over 100 genes in 11 day old plants. In addition to effector genes involved in seed maturation and reserve storage, several signaling proteins and transcription factors were identified as targets of ABI4 and/or ABI5. Although only 12% of the ABA- and ABI-dependent transcriptional targets were induced by both ABI factors in 11 day old plants, 40% of those normally expressed in seeds had reduced transcript levels in both abi4 and abi5 mutants. Surprisingly, many of the ABI4 transcriptional targets do not contain the previously characterized ABI4 binding motifs, the CE1 or S box, in their promoters, but some of these interact with ABI4 in electrophoretic mobility shift assays, suggesting that sequence recognition by ABI4 may be more flexible than known canonical sequences. Yeast one-hybrid assays demonstrated synergistic action of ABI4 with ABI5 or related bZIP factors in regulating these promoters, and mutant analyses showed that ABI4 and these bZIPs share some functions in plants.