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.

Abscisic acid induces stomatal closure in horsetails

“…Equisetum pratense consistently exhibited the lowest values of stomatal conductance. In accordance, the values of steady-state pretreatment transpiration of horsetails remained well below 1 mmol m À2 s À1 , whereas Arabidopsis transpiration in the respective conditions was c. 2 mmol m À2 s À1 (Tulva et al, 2023). Relatively low values of transpiration and stomatal conductance of horsetails and ferns have been associated with their lower stomatal density (Franks & Beerling, 2009;K€ ubarsepp et al, 2020;Wuyun et al, 2023), reduced hydraulic conductance (Brodribb et al, 2005) and relatively large investment into secondary metabolites (Cândido-Sobrinho et al, 2022).…”

Low relative air humidity and increased stomatal density independently hamper growth in young Arabidopsis

“…However, in our recent study, growth under low RH was not more impaired in the ost1 mutant with large stomatal conductance than in wild-type plants (Tulva et al 2023) . As the ost1 mutant is deficient in stomatal closure in response to low humidity, the lack of stronger growth impairment than in wild-type plants cannot be explained by stomatal closure in response to low RH.…”

“…Experiments addressing the effects of low air humidity help to address the role of increased evaporative demand on plant growth. Low night-time relative humidity did not affect biomass production in Arabidopsis (Christman, Donovan & Richards 2009) , whereas we recently found that low air humidity applied both during the day and night hampered plant growth in both wild-type plants and mutants with increased stomatal conductance due to larger stomatal apertures (Tulva, Välbe & Merilo 2023) .…”