Receptor‐like kinases (RLKs) represent the largest group of cell surface receptors in plants. The monophyletic leucine‐rich repeat (LRR)‐RLK subfamily II is considered to contain the somatic embryogenesis receptor kinases (SERKs) and NSP‐interacting kinases known to be involved in developmental processes and cellular immunity in plants. There are only a few published studies on the phylogenetics of LRR‐RLKII; unfortunately these suffer from poor taxon/gene sampling. Hence, it is not clear how many and what main clades this family contains, let alone what structure–function relationships exist. We used 1342 protein sequences annotated as ‘SERK’ and ‘SERK‐like’ plus related sequences in order to estimate phylogeny within the LRR‐RLKII clade, using the nematode protein kinase Pelle as an outgroup. We reconstruct five main clades (LRR‐RLKII 1–5), in each of which the main pattern of land plant relationships re‐occurs, confirming previous hypotheses that duplication events happened in this gene subfamily prior to divergence among land plant lineages. We show that domain structures and intron–exon boundaries within the five clades are well conserved in evolution. Furthermore, phylogenetic patterns based on the separate LRR and kinase parts of LRR‐RLKs are incongruent: whereas the LRR part supports a LRR‐RLKII 2/3 sister group relationship, the kinase part supports clades 1/2. We infer that the kinase part includes few ‘radical’ amino acid changes compared with the LRR part. Finally, our results confirm that amino acids involved in each LRR‐RLKII–receptor complex interaction are located at N‐capping residues, and that the short amino acid motifs of this interaction domain are highly conserved throughout evolution within the five LRR‐RLKII clades.

中文翻译：

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富含亮氨酸的重复受体样激酶II的系统发育学揭示了整个植物界的五个主要进化枝。

受体样激酶（RLK）代表植物中最大的细胞表面受体。一元富含亮氨酸的重复序列（LRR）-RLK子家族II被认为含有已知与植物发育过程和细胞免疫有关的体细胞胚发生受体激酶（SERK）和NSP相互作用激酶。关于LRR-RLKII的系统发育学的研究很少。不幸的是，这些人遭受不良的分类/基因采样。因此，尚不清楚该家族包含多少个主要进化枝，更不用说存在什么结构-功能关系了。为了估计LRR-RLKII进化枝内的系统发育，我们使用了线虫蛋白激酶Pelle作为外群，使用了1342个蛋白质序列标注为'SERK'和'SERK-like'以及相关序列。我们重建了五个主要分支（LRR‐RLKII 1-5），在每种情况下，陆生植物关系的主要模式均会再次出现，从而证实了先前的假设，即在陆生植物世系之间出现分歧之前，该基因亚家族发生了重复事件。我们证明了五个进化枝内的结构域结构和内含子-外显子边界在进化中非常保守。此外，基于LRR-RLKs的单独LRR和激酶部分的系统发育模式是不一致的：虽然LRR部分支持LRR-RLKII 2/3姐妹组关系，但激酶部分支持进化枝1/2。我们推断，与LRR部分相比，激酶部分几乎没有“自由基”氨基酸变化。最后，我们的结果证实，每个LRR-RLKII-受体复合物相互作用中涉及的氨基酸都位于N帽残基上，