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

Abstract 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.