Chemical disruption of ABA signaling overcomes high-temperature inhibition of seed germination and enhances seed priming responses

Seed germination is critical to agricultural productivity because low germination rates and/or asynchronous germination negatively affect stand establishment and subsequent yields. Exposure to high temperatures during seed imbibition can decrease both germination synchrony and rates through an ABA-mediated process called thermoinhibition. Methods to reduce thermoinhibition would be agriculturally valuable, particularly with increasing global mean temperatures. Lettuce seed germination is particularly sensitive to high temperatures and is a classic system for studying thermoinhibition. Extensive evidence using mutants and carotenoid biosynthetic inhibitors (e.g. fluridone) has demonstrated that endogenous abscisic acid (ABA) biosynthesis is required for thermoinhibition in lettuce and Arabidopsis. Although fluridone and related carotenoid biosynthetic inhibitors block thermoinhibition, they are not well-suited for this application due to their herbicidal effects. Here we explore the potential of ABA receptor antagonism to disrupt thermoinhibition using antabactin (ANT), a broad-spectrum high-affinity receptor antagonist. We show low μM ANT treatments (10 μM) during lettuce seed imbibition reduces thermoinhibition at temperatures of up to 40°C, demonstrating that ABA signaling is required for thermoinhibition and that receptor antagonists are well-suited anti-thermoinhibition agents. We further explored interactions between ANT and seed priming, which is used commercially to improve seed germination and reduce thermoinhibition and is achieved by partial hydration and subsequent desiccation of seeds. We show that co-priming with ANT improves germination at elevated temperatures better than priming alone, and thus, the two treatments can be combined to improve germination. Our data demonstrate that ABA antagonists are potentially useful agrochemical leads for mitigating the effects of high temperatures on seed germination and stand establishment that may be of increasing importance due to climate change. More generally, ABA antagonists should be useful in physiological processes where ABA's effects are counterproductive to yield.