Cloning of a Conserved Receptor-Like Protein Kinase Gene and Its Use as a Functional Marker for Homoeologous Group-2 Chromosomes of the Triticeae Species

Bi Qin,Haiyan Wang,Chunmei Yu,Liping Xing,Jianhui Ji,Daowen Wang,Peidu Chen,Dajun Liu,Xueluan Chen,Aizhong Cao,Hongqing Ling,Jin Xiao,Xiue Wang,Tingting Chen,Wengui Yan

doi:10.1371/journal.pone.0049718

Abstract

Receptor-like kinases (RLKs) play broad biological roles in plants. We report on a conserved receptor-like protein kinase (RPK) gene from wheat and other Triticeae species. The TaRPK1 was isolated from the Triticum aestivum cv. Prins - Triticum timopheevii introgression line IGVI-465 carrying the powdery mildew resistance gene Pm6. The TaRPK1 was mapped to homoeologous chromosomes 2A (TaRPK1-2A), 2D (TaRPK1-2D) and the Pm6-carrier chromosome 2G (TaRPK1-2G) of IGVI-465. Under the tested conditions, only the TaRPK1-2G allele was actively transcribed, producing two distinct transcripts via alternative splicing. The predicted 424-amino acid protein of TaRPK1-2G contained a signal peptide, a transmembrane domain and an intracellular serine/threonine kinase domain, but lacked a typical extracellular domain. The expression of TaRPK1-2G gene was up-regulated upon the infection by Blumeria graminis f.sp. tritici (Bgt) and treatment with methyl jasmonate (MeJA), but down-regulated in response to treatments of SA and ABA. Over-expression of TaRPK1-2G in the powdery mildew susceptible wheat variety Prins by a transient expression assay showed that it slightly reduced the haustorium index of the infected Bgt. These data indicated that TaRPK1-2G participated in the defense response to Bgt infection and in the JA signaling pathway. Phylogenetic analysis indicated that TaRPK1-2G was highly conserved among plant species, and the amino acid sequence similarity of TaRPK1-2G among grass species was more than 86%. Based on its conservation, the RPK gene-based STS primers were designed, and used to amplify the RPK orthologs from the homoeologous group-2 chromosomes of all the tested Triticeae species, such as chromosome 2G of T. timopheevii, 2R of Secale cereale, 2H of Hordeum vulgare, 2S of Aegilops speltoides, 2Sl of Ae. longissima, 2Mg of Ae. geniculata, 2Sp and 2Up of Ae. peregrina. The developed STS markers serve as conserved functional markers for the identification of homoeologous group-2 chromosomes of the Triticeae species.

Highlights

Receptor protein kinases (RPKs) play essential roles in the signal perception in animals in response to various growth factors and hormones [1]
The results indicated that TaRPK1-2G was highly conserved among the selected species, and the amino acid sequence identity in the kinase domain was more than 86% among the RPKs from various grass species, including wheat (TaRPK1-2G), barley (HvRPK), Oryza sativa (OsRPK), Brachypodium distachyon (BdRPK), Sorghum bicolor (SbRPK), Setaria italica (SiRPK), Zea mays (ZmRPK), and Panicum virgatum (PavRPK) (Figure 4, detail information on these orthologs were provided in Form S1)
Comparative genome mapping of the TaRPK1-2G orthologs in grass species showed that they were well retained in the collinear regions of TaRPK1-2G which have been revealed by wholegenome comparison [28,29], such as TaRPK1-2G and Pm6 colocated on 2BL [fraction length (FL) 0.50–1.00 [27], HvRPK on chromosome 2H: 140.1 cM, OsRPK on Chr4: 33,594,296 bp– 33,596,099 bp, BdRPK on Bd5: 26,167,244 bp–26,168,882 bp, and SbRPK on chromosome_6: 59,793,399 bp–59,795,140 bp (The locations of these RPKs in their corresponding genomes are shown in Form S1)

Summary

Introduction

Receptor protein kinases (RPKs) play essential roles in the signal perception in animals in response to various growth factors and hormones [1]. These receptors generally have an extracellular domain, a single transmembrane domain, and an intracellular catalytic kinase domain. Based on the primary structure, plants have a large gene family named as receptor-like kinases (RLKs) similar to the animal’s RPKs, the autophosphorylation in plant RLKs is mostly specific to the serine and/or threonine [3]. Plant RLKs include receptor kinases and receptor-like cytoplasmic kinases (RLCKs) with no typical signal sequence or transmembrane domain, which have been implicated in the perception and transduction of extracellular signals into the cell [4]. The diversity in the ligand binding domain endows the RLKs a wide range of biological function, such as growth and development, responses to biotic and abiotic stresses, and nodulation and rhizobial symbiosis [5]

Methods

Results

Conclusion