Submitted to: Molecular Genetics and Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2017
Publication Date: 1/24/2017
Publication URL: http://handle.nal.usda.gov/10113/5756070
Citation: Lu, S., Faris, J.D., Edwards, M.C. 2017. Molecular cloning and characterization of two novel genes from hexaploid wheat that encode double PR-1 domains coupled with a receptor-like protein kinase. Molecular Genetics and Genomics. 292:435-452. doi:10.1007/s00438-017-1287-3.
Interpretive Summary: The genome of bread wheat contains a large gene family consisting of estimated >60 members known as pathogenesis-related protein 1 (PR-1) genes. Twenty-three PR-1-like genes have been identified in our previous work. The main goal of this study was to continue to identify all members of the PR-1 gene family in wheat for further functional analysis. Here, we describe the cloning and characterization of two novel PR-1 genes that contain transmembrane and protein kinase domains characteristic of receptor-like protein kinases, the key components of signal transductions pathways controlling plant development, defense and stress responses. We obtained full-length DNA and mRNA sequences of the two new PR-1 genes, determined their chromosomal locations and confirmed that both genes are subjected to alternative splicing, a mechanism to generate different protein isoforms from the same gene. We also demonstrated that the two new PR-1 genes are up-regulated by pathogen attacks and abiotic stress conditions such as soil salinity and herbicide treatment frequently confronted by wheat crops. The sequence information and gene-specific primers validated in this study provide molecular tools for future genetic association mapping to reveal possible linkages between the two new PR-1 genes and phenotypic traits of interest in wheat populations. Further studies on these linkages (if any) may shed new insights into the roles of the PR-1 family in defense and stress response in plants.
Technical Abstract: Hexaploid wheat (Triticum aestivum L.) contains at least 23 TaPr-1 genes encoding the group 1 pathogenesis-related (PR-1) proteins as identified in our previous work. Here we report the cloning and characterization of TaPr-1-rk1 and TaPr-1-rk2, two novel genes closely related to the wheat PR-1 family. The two TaPr-1-rk genes are located on homoeologous chromosomes 3D and 3A, respectively, and each contains a large open reading frame (7,562 or 6,236 bp) that is interrupted by seven introns and subjected to alternative splicing (AS) with five or six isoforms of mRNA transcripts. The deduced full-length TaPR-1-RK1 and TaPR-1-RK2 proteins (95% identity) contain two repeat PR-1 domains, the second of which is fused via a transmembrane helix to a serine/threonine kinase catalytic (STKc) domain characteristic of receptor-like protein kinases. Phylogenetic analysis indicated that the two PR-1 domains of the TaPR-1-RK proteins form sister clades with their homologues identified in other monocot plants and are well separated from stand-alone PR-1 proteins, whereas the STKc domains may have originated from cysteine-rich receptor-like kinases (CRKs). Reverse transcriptase-PCR analysis revealed that the TaPr-1-rk genes are predominantly expressed in wheat leaves and their expression levels are elevated in response to pathogen attacks, such as infection by barley stripe mosaic virus (BSMV), and also to stress conditions, most obviously, to soil salinity. This is the first report on PR-1-CRK hybrid proteins in wheat. The data may shed new insights into the function/evolutionary origin of the PR-1 family and the STKc-mediated defense/stress response pathways in plants.