The Flowering Time Regulator Flk Acts Through the ROS Scavenging Gene Catalase 2 in Arabidopsis Defense

Abstract

Plant defense and development are intricately interconnected. The putative RNA binding protein FLOWERING LOCUS K HOMOLOGY DOMAIN (FLK) was previously shown to play a critical role in regulating pathogen defense and flowering time. However, the molecular basis underlying the multifunctionality of FLK remains to be determined. Here we provide data to support a role of FLK in regulating reactive oxygen species (ROS) homeostasis, which is dependent on the primary catalase gene CAT2. The flk mutations conferred reduced ROS burst upon elicitation and higher resistance to ROS-inducing stress conditions, including treatments with the herbicide paraquat, UV, and high salt. These flk phenotypes were suppressed by the cat2-1 mutation. Our data further showed that CAT2 was required for flk-conferred pathogen responses. Catalase activity analysis indicated a negative regulation of the enzyme activity by FLK. Interestingly, this ROS regulatory role of FLK is independent of its function in flowering time control. Together our data illustrate a mechanism underlying FLK’s defense role and decouple the multifunctionality of FLK in defense and development in Arabidopsis.