Assessing the Diverse Functions of BAK1 and Its Homologs in Arabidopsis, beyond BR Signaling and PTI Responses

Abstract

Plants possess a variety of extracellular leucine-rich repeats receptor-like kinases (LRR-RLKs) to coordinate developmental programs with responses to environmental changes. Out of sixteen families of LRR-RLKs in Arabidopsis, the LRR-RLKII family consists of fourteen individual members, including five Arabidopsis thaliana somatic embryogenesis receptor kinases (AtSERKs). BAK1/AtSERK3 was first identified as a dual co-receptor of BRI1 and FLS2, mediating BR signaling and pathogen-associated molecular pattern (PAMP) triggered immunity (PTI), respectively. Since its identification, many researchers have attempted to elucidate the phosphorylation mechanisms between receptor complexes and identify additional components that interact with receptor complexes to transduce the signaling downstream. Relatively detailed early events in complex formation, phosphorylation sites on the BRI1/BAK1 complex and BAK1-interacting proteins, such as BIK1 and PUB13, have been identified. Small receptor complexes consisting of BAK1 and BIR1 or BAK1 and AtSERK4 regulate cell death during steady state conditions. Moreover, the redundant and distinct functions of AtSERK proteins and other members of the LRR-RLKII family have been revealed. This review focuses on the integration of the information from the most recent studies concerning BAK1 and its homologs.

An Overdose of the Arabidopsis Coreceptor BRASSINOSTEROID INSENSITIVE1-ASSOCIATED RECEPTOR KINASE1 or Its Ectodomain Causes Autoimmunity in a SUPPRESSOR OF BIR1-1-Dependent Manner

“…Thus, the rice stunted phenotype might derive from defense activation, which can negatively impact plant development in the absence of proper control mechanisms (Tian et al, 2003;Korves and Bergelson, 2004). This hypothesis is clearly supported by our new findings in Arabidopsis, showing that BAK1 overexpression (1) induces effects on plant growth different from those associated with activated or inhibited BR signaling (Choe et al, 2001;Wang et al, 2001;Kim et al, 2013), (2) triggers constitutive immunity, and (3) causes a dwarf phenotype that cannot be rescued by the bri1-301 mutation affecting BR perception (Table I). Surprisingly, the observed phenotype has not been described in most studies using BAK1 overexpression in Arabidopsis Nam and Li, 2002;Kemmerling et al, 2007;Gou et al, 2012).…”

“…On the other hand, BAK1 is widely studied as a key component of immune signaling pathways due to its known association with different PRRs, including RLKs and RLPs (Kim et al, 2013;Böhm et al, 2014). Upon MAMP perception, PRRs induce signaling and physiological defense responses like mitogen-activated protein kinase (MAPK) activation, reactive oxygen species and ethylene production, and modifications in gene expression, all of which contribute to PTI.…”

Phytosulfokine Regulates Growth in Arabidopsis through a Response Module at the Plasma Membrane That Includes CYCLIC NUCLEOTIDE-GATED CHANNEL17, H+-ATPase, and BAK1

“…Interaction studies further revealed binding of PSKR1 to BAK1. BAK1 acts as a coreceptor for a number of LRR receptor kinases, including BRI1 and FLS2 (Chinchilla et al, 2009;Postel et al, 2010;Kim et al, 2013), and binds to the bacterial effector proteins AvrPto and AvrPtoB. This latter interaction prevents binding of BAK1 to the immune receptor FLS2 and activation of immune responses (Shan et al, 2008).…”

A Mathematical Model for the Coreceptors SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE1 and SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE3 in BRASSINOSTEROID INSENSITIVE1-Mediated Signaling

“…The identification of members of the SERK family that act redundantly in different signaling pathways Li, 2010;Du et al, 2012;Gou et al, 2012;Kim et al, 2013) has underscored the importance Figure 5. Prediction of BRI1 signaling output in the absence of SERK coreceptors.…”