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Title: Isolation of ABA hypersensitive mutants in allhexaploid breadwheat

item Garland-Campbell, Kimberly
item Steber, Camille

Submitted to: Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2010
Publication Date: 6/30/2010
Citation: Abellera, J.C., Strader, L.C., Schramm, E., Garland Campbell, K.A., Steber, C.M. 2010. Isolation of ABA hypersensitive mutants in allhexaploid breadwheat. Genetics. 179:620-629.

Interpretive Summary: Preharvest sprouting (PHS) and drought are two yield limiting problems in wheat growing regions. Both of these problems are regulated by the stress hormone abscisic acid (ABA). As a first step to developing wheat germplasm with improved resistance ot PHS and drought, this study used mutation breeding to identify ABA hypersensitive mutants of wheat. Such mutants are not defined as being genetically modified because transformation with DNA was not used. It is clear that the ABA hypersensitive wheat isolated has increased seed dormancy suggesting that they may show increased tolerance to PHS. Future work will evaluate these lines for PHS and drought tolerance.

Technical Abstract: The plant hormone abscisic acid (ABA) stimulates seed dormancy during embryo maturation, inhibits germination of mature seed, and stimulates stress responses such as stomatal closure in response to drought stress. Arabidopsis mutants isolated for ABA hypersensitive (ABH) seed germination showed increased seed dormancy and drought tolerance. ABH wheat plants may provide increased resistance to preharvest sprouting (PHS) by increasing seed dormancy, and increased drought tolerance by increasing ABA sensitivity in stomatal closure. Based on this hypothesis, wheat plants hypersensitive to ABA in seed germination have isolated in fast-neutron mutagenized allohexaploid wheat (Chinese spring). Because the degree of ABA sensitivity is dependent on the dormancy status of the grain, afterripened M2 grains were screened for inability to germinate on a concentration of ABA that is too low to prevent wild type seed germination. After months of afterripening 25 of the original 84 mutants identified appeared to show increased sensitivity to ABA compared to unmutagenized Chinese spring. Of these 25, 6 mutants appeared to show a consistent phenotype. ABA dose-response assays on germinating seeds showed that four mutants increased sensitivity in a dose-dependent fashion, while two showed a high degree of embryo dormancy regardless of the concentration of ABA. Genetic analysis showed that two are the result of a single dominant mutation, one a single recessive gene, and three others may be a single co-dominant (additive) mutation. These results indicate that it is possible to identify ABA hypersensitive mutants in wheat, and suggest that this method can be used to increase grain dormancy in wheat.