The ABA Receptor Antagonist Antabactin Restores Germination of Thermoinhibited Lettuce

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. In principle, ABA biosynthetic inhibitors could be used to block thermoinhibition, but carotenoid biosynthetic inhibitors are not well-suited for this application due to their herbicidal effects and current hydroxamate ABA biosynthetic inhibitors lack potency. 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 uM ANT treatments (10uM) during seed imbibition reduce thermoinhibition at temperatures of up to 40C, demonstrating that ABA signaling is required for thermoinhibition. 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 primed lettuce seeds have improved germination rates at high temperatures, consistent with previous observations; moreover, seeds primed in the presence of ANT show further increases in germination at elevated temperatures, showing that the two treatments can be combined to improve lettuce seed germination. Our data demonstrate that ABA antagonists are candidate agrochemicals for mitigating the effects of high temperature on seed germination and stand establishment that may be of increasing importance due to climate change. ### Competing Interest Statement The authors have declared no competing interest.