The Karrikin Receptor KARRIKIN INSENSITIVE2 Positively Regulates Heat Stress Tolerance in Arabidopsis thaliana.

In this study, we investigated the potential role of the karrikin receptor KARRIKIN INSENSITIVE2 (KAI2) in the response of Arabidopsis seedlings to high temperature stress. We performed phenotypic, physiological and transcriptome analyses of Arabidopsis kai2 mutants and wild-type (WT) plants under control (kai2_C and WT_C, respectively), and 6 h and 24 h heat stress conditions (kai2_H6, kai2_H24, WT_H6, and WT_H24, respectively) to understand the basis for KAI2-regulated heat stress tolerance. We discovered that kai2 mutants exhibited hypersensitivity to high temperature stress relative to WT plants, which might be associated with more highly increased leaf surface temperature and cell membrane damage of kai2 mutant plants. Next, we performed comparative transcriptome analysis of kai2_C, kai2_H6, kai2_H24, WT_C, WT_H6 and WT_H24 to identify transcriptome differences between WT and kai2 mutant in response to heat stress. K-mean clustering of normalized gene expression separated the investigated genotypes into three clusters based on heat-treated and non-treated control conditions. Within each cluster, kai2 mutants were separated from WT plants, implying that kai2 exhibited distinct transcriptome profiles relative to WT plants. Gene ontology and KEGG enrichment analyses showed a repression in 'misfolded protein binding', 'heat shock protein binding', 'unfolded protein binding' and 'protein processing in endoplasmic reticulum' pathways, which was consistent with the down-regulation of several genes encoding heat shock proteins and heat shock transcription factors in kai2 mutant versus WT plants under control and heat stress conditions. Our findings suggest that chemical or genetic manipulation of KAI2 signaling may provide a novel way to improve heat tolerance in plants.