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Pattern-triggered immunity (PTI) is initiated when plants detect pathogen-associated molecular patterns (PAMPs) through pattern-recognition receptors (PRRs). How moderate increases in temperature affect this plant immune signalling remains unclear. We explored this by using flg22 and the leucine-rich repeat receptor kinase (LRR-RK) FLS2 as a model receptor-ligand system and Ca ²⁺ signaling as a representative PTI output. A pre-treatment at 28 °C significantly impaired the flg22-induced [Ca ²⁺ ] _cyt influx, leading to a reduced expression of calcium-dependent defence genes, ICS1 and EDS1. This effect correlated with a temperature-dependent reduction in FLS2 abundance. A qualitatively similar inhibition of these responses was observed when membrane fluidity was artificially increased using benzyl alcohol. This suggests that the effect of elevated temperature might act through changes in membrane properties. Artificially restoring FLS2 protein levels rescued flg22-dependent Ca ²⁺ signalling and ICS1 and EDS1 expression in seedlings pre-treated at 28°C or with benzyl alcohol. Together, these findings indicate that increased membrane fluidity reduces FLS2 protein levels, thereby compromising Ca ²⁺ signalling, and probably other, flg22-indcued responses. This highlights a potential mechanistic link between temperature perception, membrane fluidity, and FLS2-dependent calcium signalling, providing insight into how an increase in global temperatures may compromise plant immune responses in the future.