The Arabidopsis SUMO E3 ligase SIZ1 mediates the temperature dependent trade-off between plant immunity and growth

Increased ambient temperature is widely considered to be inhibitory to basal and effector-triggered plant immunity. For example, SNC1-dependent auto-immunity in Arabidopsis results in enhanced basal resistance at 22C, which is fully suppressed at 28C. The sumoylation mutant siz1 also displays auto-immunity at 22C. We find that its auto-immunity is sustained at 28C while still requiring PAD4/EDS1 and SNC1 function. Moreover, its rosette size does not fully recover at 28C, which is normally seen for SNC1 gain-of-function mutants. Related, thermomorphogenesis is also compromised in the SUMO mutants. This role of SIZ1 in growth regulation does not depend on PAD4 or SNC1. In corroboration, SUMO mutants show a global delay in their transcriptional profile for thermosensitive growth regulators and these differentially expressed genes show an overrepresentation for PIF4 genomic targets. This transcription factor (TF) PIF4 is the central regulator of thermomorphogenesis, while also inhibiting plant immunity at 28C. Our findings thus reveal that SUMO conjugation has a central role in PIF4 regulation prioritizing growth over immunity at elevated temperatures. Such molecular understanding of how temperature affects growth over immunity is important to mitigate the effects of climate change on agriculture

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