The Flowering Time RegulatorFLKControls Pathogen Defense inArabidopsis thaliana

Abstract

Plant disease resistance is a complex process that is maintained in an intricate balance with development. Increasing evidence indicates the importance of post-transcriptional regulation of plant defense by RNA binding proteins. The K homology (KH) repeat is an ancient RNA binding motif found in proteins from diverse organisms. The role of KH domain proteins in pathogen resistance is not well known. From a genetic screen aimed to uncover novel defense genes in Arabidopsis, we identified a new allele of the canonical flowering regulatory gene, FLOWERING LOCUS KH Domain (FLK), encoding a putative triple KH-repeat protein. In addition to late flowering, the flk mutants exhibited decreased resistance to the bacterial pathogen Pseudomonas syringae and increased resistance to the necrotrophic fungal pathogen Botrytis cinerea. We found that the flk mutations compromised basal defense and defense signaling mediated by salicylic acid and led to increased reactive oxygen species (ROS) scavenging, likely through FLK’s regulation of the ROS scavenging enzyme catalases. RNA-seq data revealed that major defense signaling genes are regulated by FLK, providing a molecular basis for FLK’s contribution to pathogen defense. Together our data support that FLK is a multifunctional protein regulating pathogen defense and development of plants.

Exploiting breakdown in nonhost effector–target interactions to boost host disease resistance

“…S11 ), several closely related family members of this RNA binding protein in Arabidopsis are known to regulate flowering time ( 60 ), suggesting an off-target action of the effector. In this regard, it is interesting to note that whereas KRBP1 acts as a susceptibility factor ( 33 ), its closely related homolog FLK is a positive regulator of flowering ( 61 ), and a recent preliminary report suggests that it is also a positive regulator of plant immunity ( 62 ). It will be interesting to see whether Pi04089 interacts with a closely related K homology (KH) RNA binding protein, such as FLK.…”

Valsa mali secretes an effector protein VmEP1 to target a K homology domain‐containing protein for virulence in apple

“…The activation of plant immunity leads to a series of reactions, including an increase in reactive oxygen species (ROS), Ca 2+ influx, mitogen‐activated protein kinase activation, and regional cell death (Boller & Felix, 2009 ; Cheng et al, 2019 ; Spoel & Dong, 2012 ; Zipfel & Oldroyd, 2017 ). Numerous proteins, such as the transcription factor BZR1, which is involved in brassinosteroid signalling (Qi et al, 2021 ), mitogen‐activated protein kinase kinases (Rufian et al, 2021 ), and FLOWERING LOCUS KH domain (FLK) (Fabian et al, 2021 ), have been reported to regulate plant immune responses. Among these, FLK is an RNA‐binding protein (RBP) that regulates plant development (Lim et al, 2004 ), the ROS‐scavenging enzyme catalase, and plant immunity (Fabian et al, 2021 ).…”

“…Numerous proteins, such as the transcription factor BZR1, which is involved in brassinosteroid signalling (Qi et al, 2021 ), mitogen‐activated protein kinase kinases (Rufian et al, 2021 ), and FLOWERING LOCUS KH domain (FLK) (Fabian et al, 2021 ), have been reported to regulate plant immune responses. Among these, FLK is an RNA‐binding protein (RBP) that regulates plant development (Lim et al, 2004 ), the ROS‐scavenging enzyme catalase, and plant immunity (Fabian et al, 2021 ). Therefore, we aimed to investigate the role of RBPs in pathogen defence and ROS regulation.…”

“…Moreover, only a few studies have correlated KH domain‐containing proteins with the plant immune response. Only A. thaliana FLK is known to regulate resistance against pathogenic bacteria (Fabian et al, 2021 ; Lim et al, 2004 ). Whether other KH domain‐containing proteins are involved in regulating host resistance is still unclear.…”