Disease relevance of ABI1

• This implicates ABI1 in wound-signalling and suggests that a common early ABA signalling pathway may function in the responses to wounding and water stress [1].
• Double mutant analysis of hos5-1 and the ABA-deficient aba1-1 as well as the ABA-insensitive abi1-1 mutant indicated that the osmotic stress hypersensitivity of hos5-1 is not affected by ABA deficiency or insensitivity [2].

High impact information on ABI1

• Moreover, activation of Ca2+ channels by H2O2 and ABA- and H2O2-induced stomatal closing are disrupted in the recessive ABA-insensitive mutant gca2 [3].
• 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 [4].
• 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 [4].
• The ABI1 gene was cloned by chromosome walking, and a missense mutation was identified in the structural gene of the abi1 mutant [4].
• Thus, the control of the phosphorylation state of cell signaling components by the ABI1 product could mediate pleiotropic hormone responses [4].

Biological context of ABI1

• This demonstrates that the signal transduction pathways for all three stimuli converge on, or close to, the ABI1 and ABI2 gene products [5].
• The deduced amino acid sequence is 55% and 54% identical to ABI1 and ABI2, respectively [6].
• Comparison of the genomic structure of the ABI1, ABI2 and AtP2C-HA genes suggests that they belong to a multigene family [6].
• Here, we show that plants expressing a mutant form of HAB1 in which Gly246 was mutated to Asp (G246D) display strong ABA insensitive phenotypes [7].
• The data suggest that this mutation localized in a conserved motif in the PP2C catalytic domain could be used in other PP2Cs to reveal their biological functions [7].

Anatomical context of ABI1

• Here, I present mutational analysis of two Arabidopsis thaliana PP2Cs, encoded by ABI1 and AtPP2C, involved in the plant stress hormone abscisic acid (ABA) signaling in maize mesophyll protoplasts [8].
• The lack of ABA-induced production of PA in PLD alpha 1-null cells results in a decrease in the association of ABI1 with the plasma membrane in response to ABA [9].
• In contrast, in the ABA-insensitive mutant abi1-1, which is impaired in stomatal closure, neither AtRac inactivation nor actin cytoskeleton disruption was observed on ABA treatment [10].

Associations of ABI1 with chemical compounds

• Thus, ABI1 and ABI2 seem to control fibrillin expression that is involved in mediating ABA-induced photoprotection [11].
• Phospholipase D alpha 1-derived phosphatidic acid interacts with ABI1 phosphatase 2C and regulates abscisic acid signaling [9].
• Deletion and site-specific mutational analyses show that arginine 73 in ABI1 is essential for PA-ABI1 binding [9].
• The Arabidopsis ABI1 and ABI2 genes encode two protein serine/threonine phosphatases 2C (PP2C) [12].
• Characterisation of the redox sensitivity of ABI1 revealed a strong enzymatic inactivation by hydrogen peroxide (H2O2) which has recently been implicated as a secondary messenger of ABA signalling [13].

Physical interactions of ABI1

• We found that some PKSs interact strongly with ABI2 whereas others interact preferentially with ABI1 [14].

Regulatory relationships of ABI1

• These results indicate that ATHB-7 is transcriptionally regulated in an ABA-dependent manner and may act in a signal transduction pathway which mediates a drought response and also includes ABI1 [15].
• Furthermore, ectopic expression of ABI3 also influenced ABI1-dependent responses that occur in wild-type vegetative tissues [16].

Other interactions of ABI1

• However, leaves of abi2 revealed in comparison to WT and abi1 enhanced fibrillin levels, pointing to a posttranscriptional control mechanism [11].
• These results suggest that ATHB6 may act downstream to both ABI1 and ABI2 in a signal transduction pathway mediating a drought stress response [17].
• Our results establish the PPI motif and the protein kinase interaction domain as novel protein interaction domains that mediate the binding between the SOS2 family of protein kinases and the ABI1/2 family of protein phosphatases [14].
• These results indicate that PA produced by PLD alpha 1 inhibits the function of the negative regulator ABI1, thus promoting ABA signaling [9].
• Arabidopsis ABA response gene ABI1: features of a calcium-modulated protein phosphatase [18].

Analytical, diagnostic and therapeutic context of ABI1

• Domain II interacted with the ABI1 protein in a yeast two-hybrid assay [19].
• We show in two complementary transient ABA-inducible gene expression assays (beta-glucuronidase and luciferase enzymatic activities and quantitative flow cytometry of green fluorescent protein) that trivalent ions specifically interact with an ABI1-dependent ABA-signaling pathway leading to gene expression [20].
• 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 [21].
• PKIII was Ca2+-indepdented, inactivated by PP2A or PP2C, had a requirement for a hydrophobic residue in the +4 position of peptide substrates, had a molecular mass by gel filtration of approximately 140 kDa, and an antibody against the rye SNF1-related PK (RKIN1) recognized a 58 kDa subunit in fractions containing PKIII [22].

References