Physcomitrella patens Has Kinase-LRR R Gene Homologs and Interacting Proteins

Plant disease resistance gene (R gene)-like sequences were screened from the Physcomitrella patens genome. We found 603 kinase-like, 475 Nucleotide Binding Site (NBS)-like and 8594 Leucine Rich Repeat (LRR)-like sequences by homology searching using the respective domains of PpC24 (Accession No. BAD38895), which is a candidate kinase-NBS-LRR (kinase-NL) type R-like gene, as a reference. The positions of these domains in the genome were compared and 17 kinase-NLs were predicted. We also found four TIR-NBS-LRR (TIR-NL) sequences with homology to Arabidopsis TIR-NL (NM_001125847), but three out of the four TIR-NLs had tetratricopeptide repeats or a zinc finger domain in their predicted C-terminus. We also searched for kinase-LRR (KLR) type sequences by homology with rice OsXa21 and Arabidopsis thaliana FLS2. As a result, 16 KLRs with similarity to OsXa21 were found. In phylogenetic analysis of these 16 KLRs, PpKLR36, PpKLR39, PpKLR40, and PpKLR43 formed a cluster with OsXa21. These four PpKLRs had deduced transmembrane domain sequences and expression of all four was confirmed. We also found 14 homologs of rice OsXB3, which is known to interact with OsXa21 and is involved in signal transduction. Protein–protein interaction was observed between the four PpKLRs and at least two of the XB3 homologs in Y2H analysis.本研究从小立碗藓（Physcomitrella patens）基因组中筛选类植物抗病基因（Plant disease resistance gene, R gene）样序列。我们以候选激酶-核苷酸结合位点-富亮氨酸重复（kinase-NBS-LRR, kinase-NL）型类R样基因PpC24（登录号BAD38895）的对应结构域为参考，通过同源性搜索，共获得603个激酶样序列、475个核苷酸结合位点（Nucleotide Binding Site, NBS）样序列以及8594个富亮氨酸重复（Leucine Rich Repeat, LRR）样序列。对这些结构域在基因组中的位置进行比对后，预测得到17个激酶-NL型序列。我们还通过与拟南芥TIR-NL（NM_001125847）进行同源性搜索，获得4个Toll/白介素-1受体同源结构域-核苷酸结合位点-富亮氨酸重复（TIR-NBS-LRR, 简称TIR-NL）样序列；但其中3个TIR-NL的预测C端区域含有四肽重复结构域或锌指结构域。此外，我们以水稻OsXa21与拟南芥FLS2的同源序列为参考，搜索激酶-LRR（kinase-LRR, KLR）型序列，最终获得16个与OsXa21相似的KLR序列。对这16个KLR的系统发育分析显示，PpKLR36、PpKLR39、PpKLR40及PpKLR43与OsXa21聚为一支。这4个PpKLR含有预测的跨膜结构域序列，且经验证这4个基因均有表达。我们还发现了14个水稻OsXB3的同源基因，已知OsXB3可与OsXa21互作并参与信号转导。酵母双杂交（Yeast Two-Hybrid, Y2H）分析显示，这4个PpKLR与至少2个XB3同源蛋白之间存在蛋白质-蛋白质相互作用。