The RLK/Pelle family of kinases

Abstract

The RLK/Pelle class of proteins kinases is composed of over 600 members in Arabidopsis. Many of the proteins in this family are receptor-like kinases (RLK), while others have lost their extracellular domains and are found as cytoplasmic kinases. Proteins in this family that are RLKs have a variety of extracellular domains that drive function in a large number of processes, from cell wall interactions to disease resistance to developmental control. This review will briefly cover the major subclasses of RLK/Pelle proteins and their roles. In addition, two specific groups on RLKs will be discussed in detail, relating recent findings in Arabidopsis and how well these conclusions have been able to be translated to agronomically important species. Finally, some details on kinase activity and signal transduction will be addressed, along with the mystery of RLK/Pelle members lacking kinase enzymatic activity.

Figure 1

Phylogenetic relationships between major kinase families in plants and animals. Green dots indicate the clade contains representative genes in plant species, while a red dot indicate the clade contains representative genes in animal species. Adapted from (Shiu and Bleecker, 2001b).

Figure 2

Phylogenetic relationships between BRI1 and related genes from selected angiosperms. The tree was generated by ClustalX using the BLAST results from residues 857–1157 of the Arabidopsis BRI1 kinase domain and viewed with NJplot. Genbank accession numbers for protein sequences are as follows: Arabidopsis BRI1 NP_195650, Pea BRI1 BAC99050, Soybean BRI1 ACJ37420, Tobacco BRI1 ABR18799, Nicotiana BRI1 ABO27628, Potato BRI1 ABO27627, Tomato BRI1 AAN85409, Rice BRI1 Os08g0342300, Wheat BRI1 ABG43096, Barley BRI1 BAD01654, Rice BRL Os09g0293500, Rice BRL Os08g0342300, Potato BRLunannotated, Arabidopsis BRL3 NP_187946, Arabidopsis BRL1 NP_175957, Rice BRL2 Os10g0114400, Arabidopsis BRL2 NP_178304, Potato BRL2unannotated.

Figure 3

Phylogenetic relationships between CLV1 and related genes from selected angiosperms. From (DeYoung et al., 2006).

Figure 4

Model for brassinosteroid signaling. In the absence of signaling, BRI1 forms constitutive homodimers held inactive by BKI1 and the BRI1 autoinhibitory domain.BIN2 actively represses BES1 and BZR1 through direct phosphorylation. Binding of brassinosteroids to the BRI1 extracellular domains relieves BKI1 inhibition and allows BRI1-BAK1 interaction and sequential trans-phosphorylation. BSKs facilitate BRI1 repression of BIN2, derepressing BES1 and BZR1, allow for brassinosteroid-responsive transcriptional control. Asterisks indicate protein phosphorylation. See text for explanation and citations.

Figure 5

Model for CLV1 signaling. CLV3 is processed by a serine protease to create the active ligand (Ito et al., 2006; Ni et al., 2010). Mature CLV3 binds to CLV1, BAM and CLV2 receptors. The CLV1 and CLV2 complexes may interact with each other. Receptor activation leads to repression of POL/PLL1, which are positive regulators of WUS transcription.