Enhanced Disease Susceptibility1 Regulates Immune Response in Lotus japonicus

<i>Enhanced disease susceptibility1</i> (<i>EDS1</i>) is a key node in the plant immune signaling network, regulating salicylic acid (SA) levels and other immune responses in <i>Arabidopsis thaliana</i>. We previously reported that modulation of SA by <i>AGD2-like defense response protein 1</i> (<i>ALD1</i>) has been shown to influence the immune response in <i>Lotus japonicus</i>, but the role of <i>LjEDS1</i> in this species remains unclear. Here, we identified and characterized the <i>LjEDS1</i> gene in <i>L. japonicus</i>. The LjEDS1 protein contains a lipase-like domain and an EP domain similar to the Arabidopsis EDS1 protein. Subcellular localization studies revealed that the LjEDS1 protein is distributed in both the cytoplasm and nucleus. Heterologous expression of <i>LjEDS1</i> in the Arabidopsis <i>ateds1</i> mutant increased resistance to <i>Pseudomonas syringae</i> pv. <i>Tomato (Pst)</i> strain DC3000. In <i>L</i>. <i>japonicus</i>, roots of the <i>ljeds1</i> mutants exhibited heightened susceptibility to <i>Ralstonia solanacearum</i>, with increased lesion areas and bacterial titers. Conversely, the overexpression of <i>LjEDS1</i> reduced the lesion areas and bacterial titers in roots infected with <i>R</i>. <i>solanacearum</i> compared to those in the wild-type. Gene expression analysis showed that <i>LjEDS1</i> regulates defense-related, basal immunity, and oxidative stress response genes in <i>L</i>. <i>japonicus</i> roots. These findings establish <i>LjEDS1</i> as an important regulator of disease resistance in <i>L</i>. <i>japonicus</i>.