Maternal Effects Govern Variable Dominance of Two Abscisic Acid Response Mutations in Arabidopsis thaliana

Abstract

Three abscisic acid (ABA)-controlled responses (seed dormancy, inhibition of germination by applied ABA, and stomatal closure) were compared in wild-type versus homo-and heterozygotes of two Arabidopsis fhaliana ABA-insensitive mutants, abil and abi2.We found that sensitivity of seeds to applied ABA is partially maternally controlled but that seed dormancy is determined by the embryonic genotype. The effeds of the abil and abiZ mutations on ABA sensitivity of seed germination ranged from recessive to nearly fully dominant, depending on the parental source of the mutant allele. This maternal effect disappeared during vegetative growth. Stomatal regulation in heterozygotes showed substantial variability, but the average water loss was intermediate between that of homozygous mutants and wild type.The phytohormone ABA can regulate many processes in plant growth and development, including embryo maturation, seed dormancy, transpiration, and adaptation to environmental stresses (Zeevaart and Creelman, 1988). Genetic analyses, using either ABA biosynthetic or response mutants, have provided support for the view that ABA is the endogenous mediator for many, but not necessarily all, of these processes (reviewed by Finkelstein and Zeevaart, 1994). Two of the best-studied responses to ABA are induction of dormancy during seed development and stomatal closure during water stress. These are, respectively, representative of slow (>30 min) and fast (<5 min) responses, which have been proposed to act through different signal transduction pathways (Zeevaart and Creelman, 1988). As expected, ABA biosynthetic mutants are defective for both of these responses, producing nondormant (in some cases, viviparous) seeds and plants prone to excessive water loss, i.e. "wilty " (Koomneef, 1986). However, ABA response mutants may be defective in either or both of these responses. To date, only two classes of response mutants have been described that are both nondormant and wilty: the abil and abi2 mutants of Arabidopsis (Koomneef et al., 1984). Mutants at either of these two loci also show reduced sensitivity to exogenous ABA for the inhibition of germination. Since these mutations affect elements common to slow and fast response pathways, the A B l l and AB12 loci are thought to be central to ABA signaling. Consequently, these two genes are targets of molecular genetic studies aimed at cloning the genes and characterizing their biochemical function. DCB-9105241.We and others have undertaken extensive physiological and genetic characterization of these mutants (reviewed by Finkelstein and Zeevaart, 1994). Such studies should provide a biological context for future molecular studies of ABI gene function. In this paper we compare water loss, seed dormancy, and ABA inhibition of germination in wild type, homozygous mutants, and heterozygotes. We were surprised to find that, although originally characterized as dominant and recessive, respectively, the abil and abi2 mutations tested range from recessive to nearly fully dominant, depending on th...

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

“…To test this hypothesis, we performed a seed germination assay on varying levels of ABA, which is known to inhibit germination (Finkelstein, 1994). Figure 1 shows that the edr1 mutant is indeed hypersensitive to exogenous ABA as the percent germination at 3 d of incubation on 0.6 mM ABA was only approximately 15% for edr1 seeds compared to greater than 50% for wild type.…”

Protein Phosphatase Activity of Abscisic Acid Insensitive 1 (ABII) Protein from Arabidopsis Thaliana

“…Moreover, the characteristics of the ABIl phosphatase activity analysed here indicate that the ABIl protein is unlikely to correspond to any of the various okadaic-sensitive (Li et al, 1994;Thiel and Blatt, 1994;Schmidt et al, 1995) or Ca*+-dependent (Luan et a\., 1993) phosphatase activities shown to regulate ionic channels in guard cells. However, abil-/ behaves as a semi-dominant gain-of-function mutation (Koornneef et al, 1984;Finkelstein, 1994) since triploid Arubidopsis (ubil-I/ AB/I/ABZ/) displays the mutant phenotypes as do ubil-1 transgenic tobacco (Armstrong et al, 1995). This more complex behaviour of the abil-1 allele in plants would suggest that abil-1, despite its lower catalytic activity, still retains the ability to complex with its cellular target(s) and thereby impedes their dephosphorylation by ABIl .…”

The Protein Phosphatase AtPP2CA Negatively Regulates Abscisic Acid Signal Transduction in Arabidopsis, and Effects of abh1 on AtPP2CA mRNA

“…5A). It has been shown previously that the dominant ABA-insensitive mutants abi1-1 and abi2-1 are sensitive to water stress conditions and impair early ABA signal transduction (Koornneef et al, 1984;Finkelstein, 1994;Leung et al, 1994Leung et al, , 1997Meyer et al, 1994;Pei et al, 1997;Allen et al, 1999). More recently, plants overexpressing the AtP2C-HAB1 protein phosphatase were also shown to exhibit increased transpiration rates (Saez et al, 2004).…”