Regulation and Role of the ArabidopsisAbscisic Acid-Insensitive 5Gene in Abscisic Acid, Sugar, and Stress Response

Abstract

Abscisic acid (ABA) and stress response from late embryonic growth through early seedling development is regulated by a signaling network that includes the Arabidopsis ABA-insensitive (ABI)5 gene, which encodes a basic leucine zipper transcription factor. We have characterized genetic, developmental, and environmental regulation of ABI5 expression. Although expressed most strongly in seeds, the ABI5 promoter is also active in vegetative and floral tissue. Vegetative expression is strongly induced by ABA, and weakly by stress treatments during a limited developmental window up to approximately 2 d post-stratification, but ABA and some stresses can induce expression in specific tissues at later stages. ABI5 expression is autoregulated in transgenic plants and yeast (Saccharomyces cerevisiae), and stress response appears to involve ABI5-dependent and -independent mechanisms. To determine whether ABI5 is necessary and/or sufficient for ABA or stress response, we assayed the effects of increased ABI5 expression on growth and gene expression. Although overexpression of ABI5 confers hypersensitivity to ABA and sugar, as previously described for ABI4 and ABI3 overexpression lines, it has relatively limited effects on enhancing ABA-responsive gene expression. Comparison of expression of eight ABI5-homologous genes shows overlapping regulation by ABI3, ABI4, and ABI5, suggestive of a combinatorial network involving positive and negative regulatory interactions.The phytohormone abscisic acid (ABA) regulates many agronomically important aspects of plant growth and development, including seed maturation, dormancy, stress tolerances, and water relations (for review, see Leung and Giraudat, 1998; Rock, 2000;. All of these processes are regulated by additional signals, including other phytohormones, stage-specific regulators, and abiotic stresses. Studies of ABA-deficient mutants have shown that ABA is an essential mediator in triggering some plant responses to abiotic stresses, including drought, salinity, and cold (Rock, 2000; Shinozaki and Yamaguchi-Shinozaki, 2000; Xiong and Zhu, 2001). Dehydration and low temperatures result in elevated levels of ABA, which, in turn, trigger the synthesis of some proteins responsible for drought or freezing tolerance. However, although most of the drought-and salt-induced genes studied to date can be induced by ABA, many aspects of stress response are also mediated by ABA-independent mechanisms (Shinozaki and Yamaguchi-Shinozaki, 2000). These results indicate that ABA participates in only part of a network of stress-signaling mechanisms. Furthermore, even the ABA-dependent portions of this network rely on both independent and partially redundant signaling components, some of which are produced only in specific developmental stages or tissues of the plant.Components of this signaling network have been identified by a combination of biochemical, cell biological, and forward and reverse genetic approaches. To date, nearly 50 loci in Arabidopsis alone have been demonstrated to function in v...

The effects of putrescine are partly overlapping with osmotic stress processes in wheat

“…Abscisic acidinsensitive 5-like protein 6, a basic leucine zipper transcription factor, which responses to a variety of stresses [31], and putative AP2 domain transcriptional regulator, a member of dehydration-responsive element-binding proteins (DREBs), which is an important plant transcription factor and regulate the expression of many stress-inducible genes mostly in an ABA-independent manner and play a critical role in improving the abiotic stress tolerance of plants [32] were also induced. However, most of the induced genes are involved in general stress responses.…”

Environmental nitrate signals through abscisic acid in the root tip

“…2), 33 raising the intriguing possibility that the transcription factor(s) that act upstream of SCR in ABI4 and ABI5 root meristem signaling are, in fact, components of the ABA/ NO 3 signaling pathway. ABI4 and ABI5 expression have long been known to be induced by ABA, [56][57][58] and nitrate modulation of root architecture requires the function of both ABI4 and ABI5, but not other ABI genes. 16 Together, these observations suggest that SCR is an integral component of the ABA signaling network regulating root growth, and that ABI4 and ABI5 function downstream of nitrate in the control of root growth.…”

Powdery Mildew Resistance Conferred by Loss of the ENHANCED DISEASE RESISTANCE1 Protein Kinase Is Suppressed by a Missense Mutation in KEEP ON GOING, a Regulator of Abscisic Acid Signaling

“…ABI5 is a key transcription factor required for the induction of many ABA-responsive genes, and is itself inducible by ABA (Lopez-Molina et al, Brocard et al, 2002). It is most highly expressed in germinating seeds (Lopez-Molina et al, 2001;Brocard et al, 2002).…”