l‐Glutamate activates salicylic acid signaling to promote stomatal closure and PR1 expression in Arabidopsis

Glutamate (l‐Glu), an animal neurotransmitter, plays an essential role in plant signaling and regulates various plant physiological responses. We previously showed that l‐Glu regulates stomatal closure in Arabidopsis via the glutamate receptor‐like 3.5 gene (GLR3.5). Here, we showed that l‐Glu activates salicylic acid (SA) signaling in Arabidopsis. l‐Glu not only promoted stomatal closure but also triggered the expression of the PR1 gene via GLR3.5. These l‐Glu‐dependent actions were strongly suppressed in SA‐insensitive npr1‐1 and SA‐deficient sid2‐2 mutants, indicating that SA is involved in l‐Glu signaling. A loss‐of‐function mutant of the gene encoding the SRK2E/OST1 kinase, which plays a pivotal role in abscisic acid signaling, was insensitive to both l‐Glu‐induced stomatal closure and PR1 expression. The glr3.5 mutants did not alleviate SA‐induced stomatal closure, indicating that SA may function downstream of GLR3.5. These results indicate that l‐Glu activates SA signaling, and that SRK2E/OST1 may play pivotal roles in such signaling.