ABI1 | GeneID:828714 | Arabidopsis thaliana

NM_118741  

AAA50237   AAN13081   BAE98668   CAA54383   CAB39673   CAB79463   CAC41208   CAW50795   CAW54043   NP_194338   P49597   T04263  

• At.21332 cluster
• Rra.24772 cluster
• Rra.28182 cluster

1. [ ] Watanabe N, et al. (2008) "BAX inhibitor-1 modulates endoplasmic reticulum stress-mediated programmed cell death in Arabidopsis." J Biol Chem. 283(6):3200-3210. PMID:18039663

The components and pathways that regulate programmed cell death (PCD) in plants remain poorly understood. Here we describe the impact of drug-induced endoplasmic reticulum (ER) stress on Arabidopsis seedlings and present evidence for the role of Arabidopsis BAX inhibitor-1 (AtBI1) as a modulator of ER stress-mediated PCD. We found that treatment of Arabidopsis seedlings with tunicamycin (TM), an inhibitor of N-linked glycosylation and an inducer of ER stress by triggering accumulation of unfolded proteins in the ER, results in strong inhibition of root growth and loss of survival accompanied by typical hallmarks of PCD such as accumulation of H(2)O(2), chromatin condensation, and oligonucleosomal fragmentation of nuclear DNA. These phenotypes are alleviated by co-treatment with either of two different chemical chaperones, sodium 4-phenylbutyrate and tauroursodeoxycholic acid, both with chaperone properties that can reduce the load of misfolded protein in the ER. Expression of AtBI1 mRNA and its promoter activity are increased dramatically prior to initiation of TM-induced PCD. Compared with wild-type plants, two AtBI1 mutants (atbi1-1 and atbi1-2) exhibit hypersensitivity to TM with accelerated PCD progression. Conversely, overexpressing AtBI1 markedly reduces the sensitivity of Arabidopsis seedlings to TM. However, alterations in AtBI1 gene expression levels do not cause a significant effect on the expression patterns of typical ER stress-inducible genes (AtBip2, AtPDI, AtCRT1, and AtCNX1). We propose that AtBI1 plays a pivotal role as a highly conserved survival factor during ER stress that acts in parallel to the unfolded protein response pathway.

2. [ ] Moes D, et al. (2008) "Nuclear localization of the mutant protein phosphatase abi1 is required for insensitivity towards ABA responses in Arabidopsis." Plant J. 54(5):806-819. PMID:18298671

ABI1, a protein phosphatase 2C, is a key component of ABA signal transduction in Arabidopsis that regulates numerous ABA responses, such as stomatal closure, seed germination and inhibition of vegetative growth. The abi1-1 mutation, so far the only characterized dominant allele for ABI1, impairs ABA responsitivity in both seeds and vegetative tissues. The site of action of ABI1 is unknown. We show that there is an essential requirement for nuclear localization of abi1 to confer insensitivity towards ABA responses. Transient analyses in protoplasts revealed a strict dependence of wild-type ABI1 and mutant abi1 on a functional nuclear localization sequence (NLS) for regulating ABA-dependent gene expression. Arabidopsis lines with ectopic expression of various abi1 forms corroborated the necessity of a functional NLS to control ABA sensitivity. Disruption of the NLS function in abi1 rescued ABA-controlled gene transcription to wild-type levels, but also attenuated abi1-conferred insensitivity towards ABA during seed germination, root growth and stomatal movement. The mutation in the PP2C resulted in a preferential accumulation of the protein in the nucleus. Application of a proteosomal inhibitor led to both a preferential nuclear accumulation of ABI1 and an enhancement of PP2C-dependent inhibitory action on the ABA response. Thus, abi1-1 acts as a hypermorphic allele, and ABI1 reprograms sensitivity towards ABA in the nucleus.

3. [ ] Kaliff M, et al. (2007) "ABA is required for Leptosphaeria maculans resistance via ABI1- and ABI4-dependent signaling." Mol Plant Microbe Interact. 20(4):335-345. PMID:17427804

Abscisic acid (ABA) is a defense hormone with influence on callose-dependent and -independent resistance against Leptosphaeria maculans acting in the RLMcol pathway. ABA-deficient and -insensitive mutants in Ler-0 background (abal-3 and abil-1) displayed susceptibility to L. maculans, along with a significantly decreased level of callose depositions, whereas abi2-1 and abi3-1 remained resistant, together with the abi5-1 mutant of Ws-0 background. Suppressor mutants of abil-1 confirmed that the L. maculans-susceptible response was due to the dominant negative nature of the abil-1 mutant. Highly induced camalexin levels made ABA mutants in Col-0 background (aba2-1, aba3-1, and abi4-1) appear resistant, but displayed enhanced susceptibility as double mutants with pad3-1, impaired in camalexin biosynthesis. beta-Aminobutyric acid (BABA) pretreatment of Ler-0 contributed to an elevated level of endogenous ABA after L. maculans inoculation. Comparisons between (RLM1co1)pad3 and rlmlLerpad3 showed that ABA and BABA enhancement of callose deposition requires induction from RLM1col. ABII, but not ABI2, was found to be involved in a feedback mechanism that modulates RLM1co, expression. Genetic analysis showed further that this feedback occurs upstream of ABI4 and that components downstream of ABI4 modulate ABIJ activity. ABA and BABA treatments of the L. maculans-susceptible callose synthase mutant pmr4 showed that ABA also induces a callose-independent resistance. Similar treatments enhanced callose depositions and induced resistance to L. maculans in oilseed rape, and BABA-induced resistance was found to be independent of salicylic acid.

4. [ ] Yoshida R, et al. (2006) "The regulatory domain of SRK2E/OST1/SnRK2.6 interacts with ABI1 and integrates abscisic acid (ABA) and osmotic stress signals controlling stomatal closure in Arabidopsis." J Biol Chem. 281(8):5310-5318. PMID:16365038

ABI1 and ABI2 encode PP2C-type protein phosphatases and are thought to negatively regulate many aspects of abscisic acid (ABA) signaling, including stomatal closure in Arabidopsis. In contrast, SRK2E/OST1/SnRK2.6 encodes an Arabidopsis SnRK2 protein kinase and acts as a positive regulator in the ABA-induced stomatal closure. SRK2E/OST1 is activated by osmotic stress as well as by ABA, but the independence of the two activation processes has not yet been determined. Additionally, interaction between SRK2E/OST1 and PP2C-type phosphatases (ABI1 and ABI2) is not understood. In the present study, we demonstrated that the abi1-1 mutation, but not the abi2-1 mutation, strongly inhibited ABA-dependent SRK2E/OST1 activation. In contrast, osmotic stress activated SRK2E/OST1 even in abi1-1 and aba2-1 plants. The C-terminal regulatory domain of SRK2E/OST1 was required for its activation by both ABA and osmotic stress in Arabidopsis. The C-terminal domain was functionally divided into Domains I and II. Domain II was required only for the ABA-dependent activation of SRK2E/OST1, whereas Domain I was responsible for the ABA-independent activation. Full-length SRK2E/OST1 completely complemented the wilty phenotype of the srk2e mutant, but SRK2E/OST1 lacking Domain II did not. Domain II interacted with the ABI1 protein in a yeast two-hybrid assay. Our results suggested that the direct interaction between SRK2E/OST1 and ABI1 through Domain II plays a critical role in the control of stomatal closure.

5. [ ] Yang Y, et al. (2006) "Fibrillin expression is regulated by abscisic acid response regulators and is involved in abscisic acid-mediated photoprotection." Proc Natl Acad Sci U S A. 103(15):6061-6066. PMID:16571665

Fibrillins are lipid-binding proteins of plastids that are induced under abiotic stress conditions. In response to environmental stress, plants generate abscisic acid (ABA) as an endogenous signal. We show that ABA treatment and fibrillin accumulation enhance the tolerance of photosystem II toward light stress-triggered photoinhibition in Arabidopsis. ABA induces fibrillin accumulation, and the ABA response regulators ABI1 and ABI2 regulate fibrillin expression. The abundance of fibrillin transcripts was specifically reduced in the ABA-insensitive abi1 mutant but not in the abi2 mutant. However, leaves of abi2 revealed in comparison to WT and abi1 enhanced fibrillin levels, pointing to a posttranscriptional control mechanism. Protein interaction analysis identified the protein phosphatase ABI2 to target the preprotein of fibrillin. Interaction was abrogated either by deleting the signal peptide of prefibrillin or by the single amino acid exchange present in the phosphatase-deficient abi2 protein. Thus, ABI1 and ABI2 seem to control fibrillin expression that is involved in mediating ABA-induced photoprotection.

6. [ ] Mishra G, et al. (2006) "A bifurcating pathway directs abscisic acid effects on stomatal closure and opening in Arabidopsis." Science. 312(5771):264-266. PMID:16614222

Terrestrial plants lose water primarily through stomata, pores on the leaves. The hormone abscisic acid (ABA) decreases water loss by regulating opening and closing of stomata. Here, we show that phospholipase Dalpha1 (PLDalpha1) mediates the ABA effects on stomata through interaction with a protein phosphatase 2C (PP2C) and a heterotrimeric GTP-binding protein (G protein) in Arabidopsis. PLDalpha1-produced phosphatidic acid (PA) binds to the ABI1 PP2C to signal ABA-promoted stomatal closure, whereas PLDalpha1 and PA interact with the Galpha subunit of heterotrimeric G protein to mediate ABA inhibition of stomatal opening. The results reveal a bifurcating signaling pathway that regulates plant water loss.

7. [ ] Saez A, et al. (2006) "Enhancement of abscisic acid sensitivity and reduction of water consumption in Arabidopsis by combined inactivation of the protein phosphatases type 2C ABI1 and HAB1." Plant Physiol. 141(4):1389-1399. PMID:16798945

Abscisic acid (ABA) plays a key role in plant responses to abiotic stress, particularly drought stress. A wide number of ABA-hypersensitive mutants is known, however, only a few of them resist/avoid drought stress. In this work we have generated ABA-hypersensitive drought-avoidant mutants by simultaneous inactivation of two negative regulators of ABA signaling, i.e. the protein phosphatases type 2C (PP2Cs) ABA-INSENSITIVE1 (ABI1) and HYPERSENSITIVE TO ABA1 (HAB1). Two new recessive loss-of-function alleles of ABI1, abi1-2 and abi1-3, were identified in an Arabidopsis (Arabidopsis thaliana) T-DNA collection. These mutants showed enhanced responses to ABA both in seed and vegetative tissues, but only a limited effect on plant drought avoidance. In contrast, generation of double hab1-1 abi1-2 and hab1-1 abi1-3 mutants strongly increased plant responsiveness to ABA. Thus, both hab1-1 abi1-2 and hab1-1 abi1-3 were particularly sensitive to ABA-mediated inhibition of seed germination. Additionally, vegetative responses to ABA were reinforced in the double mutants, which showed a strong hypersensitivity to ABA in growth assays, stomatal closure, and induction of ABA-responsive genes. Transpirational water loss under drought conditions was noticeably reduced in the double mutants as compared to single parental mutants, which resulted in reduced water consumption of whole plants. Taken together, these results reveal cooperative negative regulation of ABA signaling by ABI1 and HAB1 and suggest that fine tuning of ABA signaling can be attained through combined action of PP2Cs. Finally, these results suggest that combined inactivation of specific PP2Cs involved in ABA signaling could provide an approach for improving crop performance under drought stress conditions.

8. [ ] Larkindale J, et al. (2005) "Heat stress phenotypes of Arabidopsis mutants implicate multiple signaling pathways in the acquisition of thermotolerance." Plant Physiol. 138(2):882-897. PMID:15923322

To investigate the importance of different processes to heat stress tolerance, 45 Arabidopsis (Arabidopsis thaliana) mutants and one transgenic line were tested for basal and acquired thermotolerance at different stages of growth. Plants tested were defective in signaling pathways (abscisic acid, salicylic acid, ethylene, and oxidative burst signaling) and in reactive oxygen metabolism (ascorbic acid or glutathione production, catalase) or had previously been found to have temperature-related phenotypes (e.g. fatty acid desaturase mutants, uvh6). Mutants were assessed for thermotolerance defects in seed germination, hypocotyl elongation, root growth, and seedling survival. To assess oxidative damage and alterations in the heat shock response, thiobarbituric acid reactive substances, heat shock protein 101, and small heat shock protein levels were determined. Fifteen mutants showed significant phenotypes. Abscisic acid (ABA) signaling mutants (abi1 and abi2) and the UV-sensitive mutant, uvh6, showed the strongest defects in acquired thermotolerance of root growth and seedling survival. Mutations in nicotinamide adenine dinucleotide phosphate oxidase homolog genes (atrbohB and D), ABA biosynthesis mutants (aba1, aba2, and aba3), and NahG transgenic lines (salicylic acid deficient) showed weaker defects. Ethylene signaling mutants (ein2 and etr1) and reactive oxygen metabolism mutants (vtc1, vtc2, npq1, and cad2) were more defective in basal than acquired thermotolerance, especially under high light. All mutants accumulated wild-type levels of heat shock protein 101 and small heat shock proteins. These data indicate that, separate from heat shock protein induction, ABA, active oxygen species, and salicylic acid pathways are involved in acquired thermotolerance and that UVH6 plays a significant role in temperature responses in addition to its role in UV stress.

9. [ ] Guo Y, et al. (2002) "A calcium sensor and its interacting protein kinase are global regulators of abscisic acid signaling in Arabidopsis." Dev Cell. 3(2):233-244. PMID:12194854

The phytohormone abscisic acid (ABA) triggers an oscillation in the cytosolic Ca(2+) concentration, which is then perceived by unknown Ca(2+) binding proteins to initiate a series of signaling cascades that control many physiological processes, including adaptation to environmental stress. We report here that a Ca(2+) binding protein, SCaBP5, and its interacting protein kinase, PKS3, function as global regulators of ABA responses. Arabidopsis mutants with silenced SCaBP5 or PKS3 are hypersensitive to ABA in seed germination, seedling growth, stomatal closing, and gene expression. PKS3 physically interacts with the 2C-type protein phosphatase ABI2 (ABA-insensitive 2) and to a lesser extent with the homologous ABI1 (ABA-insensitive 1) protein. Thus, SCaBP5 and PKS3 are part of a calcium-responsive negative regulatory loop controlling ABA sensitivity.

10. [ ] Leube MP, et al. (1998) "ABI1 of Arabidopsis is a protein serine/threonine phosphatase highly regulated by the proton and magnesium ion concentration." FEBS Lett. 424(1-2):100-104. PMID:9537523

The plant hormone abscisic acid (ABA) mediates various responses such as stomatal closure, maintenance of seed dormancy, and inhibition of plant growth. All three responses are regulated by the ABI1 gene product. The ABI1 protein (ABI1p) has been characterized as a protein serine/threonine phosphatase of type 2C that is highly affected in its activity by changes in the proton and magnesium ion concentrations. In the ABA-insensitive mutant abi1 of Arabidopsis thaliana a single amino acid exchange in the primary structure results in both a dominant insensitive phenotype and a strongly reduced protein phosphatase activity in vitro by possibly impairing metal ion coordination.

11. [ ] Rodriguez PL, et al. (1998) "Protein phosphatase 2C (PP2C) function in higher plants." Plant Mol Biol. 38(6):919-927. PMID:9869399

In the past few years, molecular cloning studies have revealed the primary structure of plant protein serine/threonine phosphatases. Two structurally distinct families, the PP1/PP2A family and the PP2C family, are present in plants as well as in animals. This review will focus on the plant PP2C family of protein phosphatases. Biochemical and molecular genetic studies in Arabidopsis have identified PP2C enzymes as key players in plant signal transduction processes. For instance, the ABI1/ABI2 PP2Cs are central components in abscisic acid (ABA) signal transduction. Arabidopsis mutants containing a single amino acid exchange in ABI1 or ABI2 show a reduced response to ABA. Another member of the PP2C family, kinase-associated protein phosphatase (KAPP), appears to be an important element in some receptor-like kinase (RLK) signalling pathways. Finally, an alfalfa PP2C acts as a negative regulator of a plant mitogen-activated protein kinase (MAPK) pathway. Thus, the plant PP2Cs function as regulators of various signal transduction pathways.

12. [ ] Bertauche N, et al. (1996) "Protein phosphatase activity of abscisic acid insensitive 1 (ABI1) protein from Arabidopsis thaliana." Eur J Biochem. 241(1):193-200. PMID:8898906

Mutations at the ABI1 (abscisic acid insensitive 1) locus of the plant Arabidopsis thaliana cause a reduction in sensitivity to the plant hormone abscisic acid. The sequence of ABI1 predicts a protein composed of an N-terminal domain that contains motifs for an EF-hand Ca(2+)-binding site, and a C-terminal domain with similarities to protein serine/threonine phosphatases 2C. We report here two sets of experimental evidence that indicate that ABI1 has typical protein phosphatase 2C activity. First, expression of the ABI1 C-terminal domain partially complemented the temperature-sensitive growth defect of a Saccharomyces cerevisiae protein phosphatase 2C mutant. Second, recombinant proteins that contained the ABI1 C-terminal domain displayed in vitro phosphatase activity towards 32P-labelled casein, and this activity displayed Mg2+ or Mn2+ dependence and okadaic acid insensitivity typical of protein phosphatases 2C. Characterisation of recombinant proteins that contained various portions of ABI1 indicated that the putative EF-hand motif is unlikely to mediate Ca2+ regulation of the ABI1 phosphatase activity at physiological Ca2+ concentrations, and may represent in EF-hand analogue rather than an EF-hand homologue. The abil-l mutation appeared to cause significant reduction in the phosphatase activity of ABI1. These results are discussed in relation to the dominant phenotype of abil-l over the wild-type allele in plants, and to the possible role of ABI1 in abscisic acid signalling.

13. [ ] Mantyla E, et al. (1995) "Role of Abscisic Acid in Drought-Induced Freezing Tolerance, Cold Acclimation, and Accumulation of LT178 and RAB18 Proteins in Arabidopsis thaliana." Plant Physiol. 107(1):141-148. PMID:12228349

To study the role of abscisic acid (ABA) in development of freezing tolerance of Arabidopsis thaliana, we exposed wild-type plants, the ABA-insensitive mutant abi1, and the ABA-deficient mutant aba-1 to low temperature (LT), exogenous ABA, and drought. Exposure of A. thaliana to drought stress resulted in a similar increase in freezing tolerance as achieved by ABA treatment or the initial stages of acclimation, suggesting overlapping responses to these environmental cues. ABA appears to be involved in both LT- and drought-induced freezing tolerance, since both ABA mutants were impaired in their responses to these stimuli. To correlate enhanced freezing tolerance with the presence of stress-specific proteins, we characterized the accumulation of RAB18 and LTI78 in two ecotypes, Landsberg erecta and Coimbra, and in the ABA mutants during stress response. LT- and drought-induced accumulation of RAB18 coincided with the increase in freezing tolerance and was blocked in the cold-acclimation-deficient ABA mutants. In contrast, LT178 accumulated in all genotypes in response to LT and drought and was always present when the plants were freezing tolerant. This suggests that development of freezing tolerance in A. thaliana requires ABA-controlled processes in addition to ABA-independent factors.

14. [ ] Leung J, et al. (1994) "Arabidopsis ABA response gene ABI1: features of a calcium-modulated protein phosphatase." Science. 264(5164):1448-1452. PMID:7910981

The Arabidopsis ABI1 locus is essential for a wide spectrum of abscisic acid (ABA) responses throughout plant development. Here, ABI1 was shown to regulate stomatal aperture in leaves and mitotic activity in root meristems. The ABI1 gene was cloned and predicted to encode a signaling protein. Although its carboxyl-terminal domain is related to serine-threonine phosphatase 2C, the ABI1 protein has a unique amino-terminal extension containing an EF hand calcium-binding site. These results suggest that the ABI1 protein is a Ca(2+)-modulated phosphatase and functions to integrate ABA and Ca2+ signals with phosphorylation-dependent response pathways.

15. [ ] Meyer K, et al. (1994) "A protein phosphatase 2C involved in ABA signal transduction in Arabidopsis thaliana." Science. 264(5164):1452-1455. PMID:8197457

The plant hormone abscisic acid (ABA) mediates various responses such as stomatal closure, the maintenance of seed dormancy, and the inhibition of plant growth. All three responses are affected in the ABA-insensitive mutant abi1 of Arabidopsis thaliana, suggesting that an early step in the signaling of ABA is controlled by the ABI1 locus. The ABI1 gene was cloned by chromosome walking, and a missense mutation was identified in the structural gene of the abi1 mutant. The ABI1 gene encodes a protein with high similarity to protein serine or threonine phosphatases of type 2C with the novel feature of a putative Ca2+ binding site. Thus, the control of the phosphorylation state of cell signaling components by the ABI1 product could mediate pleiotropic hormone responses.

16. [ ] Finkelstein RR, et al. (1993) "Abscisic acid-insensitive mutations provide evidence for stage-specific signal pathways regulating expression of an Arabidopsis late embryogenesis-abundant (lea) gene." Mol Gen Genet. 238(3):401-408. PMID:8492808

An Arabidopsis homolog of the abscisic acid (ABA)-inducible cotton D19 and wheat Em genes was cloned and its expression assayed at two developmental stages in wild-type, ABA-deficient (aba) and three ABA-insensitive (abi) lines of Arabidopsis thaliana. Expression of this gene was reduced slightly in seeds of aba mutants and approximately ten-fold in abi3 mutants, but seed expression was not decreased in either abi1 or abi2 monogenic mutants. In contrast, the abi1 and abi2 mutants showed a very slight reduction of ABA inducibility in 8-day-old plants, while the responses of aba and abi3 mutants were comparable to that of wild type. Although previous studies have shown that none of the abi mutations show completely stage-specific effects, the results reported here indicate that the importance of each of the ABI loci in regulating this single gene is stage-dependent. Furthermore, the fact that none of the abi mutations show more than minor effects on exogenous ABA inducibility of the Arabidopsis D19/Em homolog in young plants suggests that an additional ABA signalling pathway may be operating during vegetative growth.

17. [ ] Gilmour SJ, et al. (1991) "Cold acclimation and cold-regulated gene expression in ABA mutants of Arabidopsis thaliana." Plant Mol Biol. 17(6):1233-1240. PMID:1834244

We have examined the cold-induced enhancement of freezing tolerance and expression of cold-regulated (cor) genes in Arabidopsis thaliana (L.) Heynh (Landsberg 'erecta') and abscisic acid (ABA)-deficient (aba) and ABA-insensitive (abi) mutants derived from it. The results indicate that the abi mutations had no apparent effect on freezing tolerance, while the aba mutations did: cold-acclimated aba mutants were markedly impaired in freezing tolerance compared to wild-type plants. In addition, it was observed that non-frozen leaves from both control and cold-treated aba mutant plants were more ion-leaky than those from corresponding wild-type plants. These data are consistent with previous observations indicating that ABA levels can affect freezing tolerance. Whether ABA has a direct role in the enhancement of freezing tolerance that occurs during cold acclimation, however, is uncertain. Several studies have suggested that ABA might mediate certain changes in gene expression that occur during cold acclimation. Our data indicate that the ABA-induced expression of three ABA-regulated Arabidopsis cor genes was unaffected in the abi2, abi3, and aba-1 mutants, but was dramatically impaired in the abi1 mutant. Cold-regulated expression of all three cor genes, however, was nearly the same in wild-type and abi1 mutant plants. These data suggest that the cold-regulated and ABA-regulated expression of the three cor genes may be mediated through independent control mechanisms.