Analysis of bark proteins in blister rust-resistant and susceptible western white pine (Pinus monticola)

Comparative proteomic profiles of Pinus monticola needles during early compatible and incompatible interactions with Cronartium ribicola

The proteomic profiles of primary needles from Cr2-resistant and cr2-susceptible Pinus monticola seedlings were analysed post Cronartium ribicola inoculation by 2-DE. One hundred-and-five protein spots exhibiting significant differential expression were identified using LC-MS/MS. Functional classification showed that the most numerous proteins are involved in defence signalling, oxidative burst, metabolic pathways, and other physiological processes. Our results revealed that differential expression of proteins in response to C. ribicola inoculation was genotype- and infection-stage dependent. Responsive proteins in resistant seedlings with incompatible white pine blister rust (WPBR) interaction included such well-characterized proteins as heat shock proteins (HSPs), reactive oxygen species (ROS) scavenging enzymes, and intermediate factors functioning in the signal transduction pathways triggered by well-known plant R genes, as well as new candidates in plant defence like sugar epimerase, GTP-binding proteins, and chloroplastic ribonucleoproteins. Fewer proteins were regulated in susceptible seedlings; most of them were in common with resistant seedlings and related to photosynthesis among others. Quantitative RT-PCR analysis confirmed HSP- and ROS-related genes played an important role in host defence in response to C. ribicola infection. To the best of our knowledge, this is the first comparative proteomics study on WPBR interactions at the early stages of host defence, which provides a reference proteomic profile for other five-needle pines as well as resistance candidates for further understanding of host resistance in the WPBR pathosystem.

A maritime pine antimicrobial peptide involved in ammonium nutrition

A large family of small cysteine-rich antimicrobial peptides (AMPs) is involved in the innate defence of plants against pathogens. Recently, it has been shown that AMPs may also play important roles in plant growth and development. In previous work, we have identified a gene of the AMP β-barrelin family that was differentially regulated in the roots of maritime pine (Pinus pinaster Ait.) in response to changes in ammonium nutrition. Here, we present the molecular characterization of two AMP genes, PpAMP1 and PpAMP2, showing different molecular structure and physicochemical properties. PpAMP1 and PpAMP2 displayed different expression patterns in maritime pine seedlings and adult trees. Furthermore, our expression analyses indicate that PpAMP1 is the major form of AMP in the tree, and its relative abundance is regulated by ammonium availability. In contrast, PpAMP2 is expressed at much lower levels and it is not regulated by ammonium. To gain new insights into the function of PpAMP1, we over-expressed the recombinant protein in Escherichia coli and demonstrated that PpAMP1 strongly inhibited yeast growth, indicating that it exhibits antimicrobial activity. We have also found that PpAMP1 alters ammonium uptake, suggesting that it is involved in the regulation of ammonium ion flux into pine roots.

Antifungal activity of a Pinus monticola antimicrobial peptide 1 (Pm-AMP1) and its accumulation in western white pine infected with Cronartium ribicola

Pinus monticola antimicrobial peptide 1 (Pm-AMP1) was expressed and purified from bacterial cell lysate and its identity and purity confirmed by Western blot analysis using the Pm-AMP1 antibody. Application of Pm-AMP1 resulted in visible hyphal growth inhibition of Cronartium ribicola , Phellinus sulphurascens , Ophiostoma montium , and Ophiostoma clavigerum 3–12 days post-treatment. Pm-AMP1 also inhibited spore germination of several other phytopathogenic fungi by 32%–84% 5 days post-treatment. Microscopic examination of C. ribicola hyphae in contact with Pm-AMP1 showed distinct morphological changes. Seven western white pine ( Pinus monticola Douglas ex D. Don) families (Nos. 1, 2, 5, 6, 7, 8, 10) showing partial resistance to C. ribicola in the form of bark reaction (BR) were assessed by Western immunoblot for associations between Pm-AMP1 accumulation and family, phenotype, canker number, and virulence of C. ribicola. There was a significant difference (p < 0.001) in mean Pm-AMP1 protein accumulation between families, with higher levels detected in the full-sib BR families (Nos. 1, 2, 5) than the half-sib BR families (Nos. 6, 7). Family 8, previously described as a Mechanism ‘X’ BR family, had the highest number of BR seedlings and displayed high Pm-AMP1 levels, whereas the susceptible family (No. 10) showed the lowest levels (p < 0.05). Family 1 showed a significant association between Pm-AMP1 accumulation and overall seedling health (p < 0.01, R = 0.533), with higher protein levels observed in healthy versus severely infected seedlings. In general, low Pm-AMP1 levels were observed with an increase in the number of cankers per seedling (p < 0.05), and seedlings inoculated with the avirulent source of C. ribicola showed significantly higher Pm-AMP1 levels (p < 0.05) in the majority of BR families. Cis-acting regulatory elements, such as CCAAT binding factors, and an AG-motif binding protein were identified in the Pm-AMP1 promoter region. Multiple polymorphic sites were identified within the 5′ untranslated region and promoter regions. Our results suggest that Pm-AMP1 is involved in the western white pine defense response to fungal infection, as observed by its antifungal activity on C. ribicola and a range of phytopathogens as well as through its association with different indicators of resistance to C. ribicola.

Expression profiling of a complex thaumatin-like protein family in western white pine

The protein content in the plant apoplast is believed to change dramatically as a result of host defense response upon infection with various pathogens. In this study, six novel thaumatin-like proteins (TLPs) were identified in western white pine (Pinus monticola) needle apoplast by a proteomic strategy using two-dimensional protein electrophoresis followed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Sequent cDNA cloning found that ten P. monticola TLP genes (PmTLP-L1 to -L6 and -S1 to -S4) were expressed in various tissues. Phylogenetic analysis demonstrated that these PmTLP genes belong to a large, complex, and highly diverse plant TLP family. Quantitative reverse transcription-polymerase chain reaction (RT-qPCR) using gene-specific primer pairs showed that each PmTLP gene exhibited a characteristic pattern of mRNA expression based on their unique organ distribution, seasonal regulation, and response to abiotic and biotic stresses. A time-course analysis at the early stages of infection by white pine blister rust pathogen Cronartium ribicola revealed that a coordinated upregulation of multiple PmTLP genes was involved in P. monticola major gene (Cr2) resistance. The structural and expressional differentiations suggest that the PmTLP family may contribute to host defense as well as other mechanism.

Proteomic comparison of needles from blister rust-resistant and susceptible Pinus strobus seedlings reveals upregulation of putative disease resistance proteins

In order to characterize a hypersensitive-like reaction in selected Pinus strobus seedlings to Cronartium ribicola, a proteomic comparison of needles from resistant and susceptible seedlings was undertaken using two-dimensional gel electrophoresis (2-DE). The results revealed 19 polypeptides specific to resistant seedlings and seven of these specific to infected resistant seedlings. There were 13 polypeptides up-regulated (> or = 3-fold increase) in resistant family P327 in comparison to needle tissue from susceptible and mock-inoculated seedlings. Electrospray ionization liquid chromatography and tandem mass spectrometry was used to sequence 11 proteins from the 2-DE gels. Sequences obtained from electrospray ionization liquid chromatography and tandem mass spectrometry were used for MS-BLAST and Pro-ID database searches allowing identification with a 95 to 99% confidence level. Six proteins were determined to be homologs of proteins with known roles in disease resistance, five were determined to be homologs of members of the leucine-rich repeat (LRR) superfamily, and one was a homolog of heat shock protein 90, a protein that serves as a cofactor for certain LRR proteins. This is the first report of members of the LRR family with functional homologs in Pinus strobus and of a molecular basis for white pine blister rust resistance in Pinus strobus.

Cloning and Characterization of a Putative Antifungal Peptide Gene (Pm-AMP1) in Pinus monticola

ABSTRACT We have been working on proteins that are involved in the defense response of western white pine (WWP) (Pinus monitcola) to the blister rust fungus Cronartium ribicola. Our objective was to identify candidate genes that could be used for improving resistance of WWP to this rust pathogen. During proteomic analysis of bark proteins extracted from WWP trees exhibiting slow-canker-growth (SCG) resistance, a 10.6-kDa peptide, termed Pm-AMP1, was found to be enriched at the receding canker margin. The cDNA encoding this peptide was cloned and characterized. A BLASTX search revealed that the Pm-AMP1 encoded by its cDNA has a 50% homology with MiAMP1, a broad-spectrum antifungal protein isolated from Macadamia integrifolia. Based on the deduced amino acid sequence, an antibody was produced against the Pm-AMP1. Immunochemical quantification of the Pm-AMP1 in bark samples of susceptible WWP trees revealed this protein to be barely detectable in the cankered tissues, but occurring in higher concentrations in healthy tissues away from canker margins. Foliage of SCG-resistant trees contained higher concentrations of the Pm-AMP1 than foliage from susceptible cankered trees. Both wounding and methyl jasmonate treatment of WWP needles induced the expression of this protein, further supporting its putative role as a defense response protein.

The mode of action of the plant antimicrobial peptide MiAMP1 differs from that of its structural homologue, the yeast killer toxin WmKT

The plant antimicrobial peptide MiAMP1 from Macadamia integrifolia and the yeast killer toxin peptide WmKT from Williopsis mrakii are structural homologues. Comparative studies of yeast mutants were performed to test their sensitivity to these two antimicrobial peptides. No differences in susceptibility to MiAMP1 were detected between wild-type and several WmKT-resistant mutant yeast strains. A yeast mutant MT1, resistant to MiAMP1 but unaffected in its susceptibility to plant defensins and hydrogen peroxide, also did not show enhanced tolerance towards WmKT. It is therefore probable that the Greek key beta-barrel structure shared by MiAMP1 and WmKT provides a robust structural framework ensuring stability for the two proteins but that the specific action of the peptides depends on other motifs.

Altered fungal sensitivity to a plant antimicrobial peptide through over-expression of yeast cDNAs

A yeast cDNA expression library was screened to identify genes and cellular processes that influence fungal sensitivity to a plant antimicrobial peptide. A plasmid-based, GAL1 promoter-driven yeast cDNA expression library was introduced into a yeast genotype susceptible to the antimicrobial peptide MiAMP1 purified from Macadamia integrifolia. Following a screen of 20,000 cDNAs, three yeast cDNAs were identified that reproducibly provided transformants with galactose-dependent resistance to MiAMP1. These cDNAs encoded a protein of unknown function, a component (VMA11) of the vacuolar H(+)-ATPase and a component (cytochrome c oxidase subunit VIa) of the mitochondrial electron transport chain, respectively. To identify genes that increased sensitivity to MiAMP1, the yeast cDNA expression library was introduced into a yeast mutant with increased resistance to MiAMP1. From 11,000 cDNAs screened, two cDNA clones corresponding to a ser/thr kinase and a ser/thr phosphatase reproducibly increased MiAMP1 susceptibility in the mutant in a galactose-dependent manner. Deletion mutants were available for three of the five genes identified but showed no change in their sensitivity to MiAMP1, indicating that these genes could not be detected by screening of yeast deletion mutant libraries. Yeast cDNA expression library screening therefore provides an alternative approach to gene deletion libraries to identify genes that can influence the sensitivity of fungi to plant antimicrobial peptides.

Isolation, genetic variation and expression of TIR-NBS-LRR resistance gene analogs from western white pine ( Pinus monticola Dougl. ex. D. Don.)

Western white pine ( Pinus monticola Dougl. ex. D. Don., WWP) shows genetic variation in disease resistance to white pine blister rust ( Cronartium ribicola). Most plant disease resistance (R) genes encode proteins that belong to a superfamily with nucleotide-binding site domains (NBS) and C-terminal leucine-rich repeats (LRR). In this work a PCR strategy was used to clone R gene analogs (RGAs) from WWP using oligonucleotide primers based on the conserved sequence motifs in the NBS domain of angiosperm NBS-LRR genes. Sixty-seven NBS sequences were cloned from disease-resistant trees. BLAST searches in GenBank revealed that they shared significant identity to well-characterized R genes from angiosperms, including L and M genes from flax, the tobacco N gene and the soybean gene LM6. Sequence alignments revealed that the RGAs from WWP contained the conserved motifs identified in angiosperm NBS domains, especially those motifs specific for TIR-NBS-LRR proteins. Phylogenic analysis of plant R genes and RGAs indicated that all cloned WWP RGAs can be grouped into one major branch together with well-known R proteins carrying a TIR domain, suggesting they belong to the subfamily of TIR-NBS-LRR genes. In one phylogenic tree, WWP RGAs were further subdivided into fourteen clusters with an amino acid sequence identity threshold of 75%. cDNA cloning and RT-PCR analysis with gene-specific primers demonstrated that members of 10 of the 14 RGA classes were expressed in foliage tissues, suggesting that a large and diverse NBS-LRR gene family may be functional in conifers. These results provide evidence for the hypothesis that conifer RGAs share a common origin with R genes from angiosperms, and some of them may play important roles in defense mechanisms that confer disease resistance in western white pine. Ratios of non-synonymous to synonymous nucleotide substitutions (Ka/Ks) in the WWP NBS domains were greater than 1 or close to 1, indicating that diversifying selection and/or neutral selection operate on the NBS domains of the WWP RGA family.