Abscisic Acid Can Play a Dual Role in the <i>Triticum aestivum</i>–<i>Stagonospora nodorum</i> Pathosystem

Abscisic acid (ABA) is not only important for plant responses to abiotic stresses, but also plays a key and multifaceted role in plant immunity. In this work, we analyzed the role of ABA in the development of resistance/susceptibility in the wheat (<i>Triticum aestivum</i> L.)–<i>Stagonospora nodorum</i> Berk. pathosystem, which includes the recognition of the necrotic effectors (NEs) of a pathogen by the corresponding wheat susceptibility genes. We studied the interaction of the <i>S. nodorum</i> SnB isolate, which produces two NEs, SnToxA and SnTox3, with three wheat genotypes having different combinations of the corresponding host susceptibility genes (<i>Tsn1</i> and <i>Snn3-B1</i>). The results of this work on the gene expression and redox status of resistant and sensitive wheat genotypes treated with ABA show that ABA signaling is directed at inducing the resistance of wheat plants to <i>S. nodorum</i> SnB isolate through the activation of the early post-invasive defense genes <i>TaERD15</i> and <i>TaABI5.</i> The induction of the expression of these genes leads to reactive oxygen species (ROS) accumulation during the early stage of infection, with the subsequent limitation of the pathogen’s growth. In the presence of a compatible interaction of SnTox3<i>–Snn3-B1</i>, ABA signaling is suppressed. On the contrary, in the presence of a compatible interaction of <i>SnToxA–Tsn1</i>, ABA signaling is activated, but the activity of the early post-invasive defense genes <i>TaERD15</i> and <i>TaABI5</i> is inhibited, and the expression of the NAC (NAM, ATAF1/2, and CUC2) transcription factor (TF) family genes <i>TaNAC29</i> and <i>TaNAC21/22</i> is induced. The TF genes <i>TaNAC29</i> and <i>TaNAC21/22</i> in the presence of SnToxA induce the development of the susceptibility of wheat plants to <i>S. nodorum</i> SnB, associated with a decrease in the oxidative burst during the early stage of infection. Thus, our study provides new data on the role of the NEs SnTox3 and SnToxA in manipulating ABA signaling in the development of the susceptibility of wheat to <i>S. nodorum</i>. Deepening our knowledge in this area will be instrumental for developing new strategies for breeding programs and will contribute to the development of environmentally friendly sustainable agriculture.