Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2016
Publication Date: 9/12/2016
Citation: Martinez, S.A., Tuttle, K.M., Takebayashi, Y., Seo, M., Garland Campbell, K.A., Steber, C.M. 2016. The wheat ABA hypersensitive ERA8 mutant is associated with increased preharvest sprouting tolerance, altered hormone sensitivity and accumulation. Euphytica. doi:10.1007/s10681-016-1763-6. Interpretive Summary: This paper examines the hormonal mechanisms that allow the soft white spring wheat line Zak ERA8 to resist preharvest sprouting, the germination of grain on the mother plant when rainy conditions occur before harvest. Preharvest sprouting causes financial losses from farmers and distributors due to loss of end-use quality. Consumer confidence in the end-use quality of U.S. wheat is essential to maintaining our foreign markets. Thus, this research examined the association between grain hormones such as ABA, jasmonic acid, and auxin, in maintaining grain dormancy and resistance to preharvest sprouting. This study found that preharvest sprouting resistance was connected to higher ABA hormone sensitivity and lower GA hormone sensitivity. The long term plan is to take advantage of these connections between hormone signaling and grain dormancy to select preharvest sprouting resistance in white wheat.
Technical Abstract: Wheat preharvest sprouting (PHS) is the germination of mature grain on the mother plant when rain occurs before harvest. Higher abscisic acid (ABA) hormone levels and sensitivity are associated with higher seed dormancy and PHS tolerance. Consistent with this, the ABA hypersensitive ERA8 (Enhanced Response to ABA8) mutant resulted in increased dormancy and PHS tolerance in soft white spring wheat ‘Zak’. ERA8 seeds were initially less responsive to germination-rescue by the hormone gibberellin (GA). ERA8 gained GA and lost ABA sensitivity more slowly than wild-type during dormancy loss through after-ripening and cold imbibition. This study examined if increased ABA sensitivity in ERA8 likely resulted from increased ABA signaling or increased ABA hormone levels. Zak ERA8 had higher initial grain dormancy although endogenous embryo ABA levels were similar in Zak ERA8 and wild-type, suggesting that increased dormancy was due to increased ABA signaling rather than increased ABA accumulation. ABA levels declined with Zak ERA8 after-ripening, suggesting that ABA turnover is not defective. Elevated ERA8 dormancy was also associated with increased embryonic jasmonic acid-Ile and aleurone indole-3-acetic acid (IAA) levels. The increased IAA accumulation associated with increased grain dormancy suggests a connection between auxin and ABA signaling in wheat.