The Arabidopsis lectin EULS3 is involved in stomatal closure

•Arabidopsis EULS3 lectin interacts with ATS3A in closed stomata.•Plants with reduced ArathEULS3 expression exhibited an aberrant stomatal closure.•Pseudomonas syringae infection of wild type plants increases lectin expression.•Overexpression lines show reduction of Pseudomonas syringae disease symptoms. Plants synthesize carbohydrate binding proteins in response to adverse environmental conditions such as drought, heat, pathogen attack, etc. The Arabidopsis EULS3 lectin (referred to as ArathEULS3, encoded by At2g39050) has recently been linked to the drought stress response. In this study, endogenous binding partners for this protein have been investigated. Tandem affinity purifications and mass spectrometry analyses allowed the identification of two putative interacting proteins, Embryo-specific protein 3A (ATS3A, At2g41475) and Embryo-specific protein 3B (ATS3B, At5g62200). Bimolecular fluorescence complementation experiments confirmed the interaction between ArathEULS3 and ATS3B in closed stomata of Nicotiana benthamiana plants. Transgenic lines with reduced ArathEULS3 expression exhibited an aberrant ABA-induced stomatal closure compared to plants overexpressing ArathEULS3 and control plants suggesting a role for ArathEULS3 in ABA-induced stomatal closure. Stomata are known as the major route for Pseudomonas syringae entry into the plant tissues. Bacterial infection of wild type Arabidopsis thaliana plants was accompanied by a 6-fold increase of transcript levels for ArathEULS3. Furthermore, infection experiments with ArathEULS3 overexpression lines resulted in a clear reduction of P. syringae disease symptoms whereas plants with reduced ArathEULS3 expression showed the highest levels of leaf damage at 3 days post infection. These data point towards the physiological importance of ArathEULS3 for stomatal movement.