Gene Cloning and Tissue Expression Analysis of a PR-5 Thaumatin-Like Protein in Phellinus weirii-Infected Douglas-Fir

Transcriptional response of grapevine to infection with the fungal pathogen Lasiodiplodia theobromae

Botryosphaeria dieback on the grapevine is caused by Botryosphaeriaceae fungi, which threatens the yield and quality of grapes. At present, chemical control strategies are often observed to be ineffective in controlling the disease worldwide. Improving our understanding of the molecular mechanisms that confer resistance to pathogens would facilitate the development of more pathogen-tolerant grape varieties. Here, we used RNA sequencing analysis to profile the transcriptome of grapevine green shoots infected with Lasiodiplodia theobromae over a time course of 4, 8 and 12 hours post inoculation. A total of 5181 genes were identified as differentially expressed genes (DEGs), and DEGs were more abundant over time. Further analysis revealed that many of these DEGs are involved in plant-pathogen interactions, hormone signal transduction and phenylpropanoid biosynthesis pathways, suggesting that innate immunity, phytohormone signaling and many phenylpropanoid compounds, which constitute a complex defense network in plants, are involved in the response of grapevine against to L. theobromae infection. This study provides novel insights into the molecular mechanisms of plant-pathogen interactions that will be valuable for the genetic improvement of grapevines.

Plant antifungal proteins and their applications in agriculture

Fungi are far more complex organisms than viruses or bacteria and can develop numerous diseases in plants that cause loss of a substantial portion of the crop every year. Plants have developed various mechanisms to defend themselves against these fungi which include the production of low-molecular-weight secondary metabolites and proteins and peptides with antifungal activity. In this review, families of plant antifungal proteins (AFPs) including defensins, lectins, and several others will be summarized. Moreover, the application of AFPs in agriculture will also be analyzed.

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.

Thaumatin-like proteins are differentially expressed and localized in phloem tissues of hybrid poplar

BACKGROUND

Two thaumatin-like proteins (TLPs) were previously identified in phloem exudate of hybrid poplar (Populus trichocarpa x P. deltoides) using proteomics methods, and their sieve element localization confirmed by immunofluorescence. In the current study, we analyzed different tissues to further understand TLP expression and localization in poplar, and used immunogold labelling to determine intracellular localization.

RESULTS

Immunofluorescence using a TLP antiserum confirmed the presence of TLP in punctate, organelle-like structures within sieve elements. On western blots, the antiserum labeled two constitutively expressed proteins with distinct expression patterns. Immunogold labelling suggested that TLPs are associated with starch granules and starch-containing plastids in sieve elements and phloem parenchyma cells. In addition, the antiserum recognized TLPs in the inner cell wall and sieve plate region of sieve elements.

CONCLUSIONS

TLP localization in poplar cells and tissues is complex. TLP1 is expressed predominantly in tissues with a prominent vascular system such as midveins, petioles and stems, whereas the second TLP is primarily expressed in starch-storing plastids found in young leaves and the shoot apex.

The superfamily of thaumatin-like proteins: its origin, evolution, and expression towards biological function

Thaumatin-like proteins (TLPs) are the products of a large, highly complex gene family involved in host defence and a wide range of developmental processes in fungi, plants, and animals. Despite their dramatic diversification in organisms, TLPs appear to have originated in early eukaryotes and share a well-defined TLP domain. Nonetheless, determination of the roles of individual members of the TLP superfamily remains largely undone. This review summarizes recent advances made in elucidating the varied TLP activities related to host resistance to pathogens and other physiological processes. Also discussed is the current state of knowledge on the origins and types of TLPs, regulation of gene expression, and potential biotechnological applications for TLPs.

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.

Ultrastructural studies of Phellinus sulphurascens infection of Douglas-fir roots and immunolocalization of host pathogenesis-related proteins

Interactions between roots of Douglas-fir (DF; Pseudotsuga menziesii) seedlings and the laminated root rot fungus Phellinus sulphurascens were investigated using scanning and transmission electron microscopy and immunogold labelling techniques. Scanning electron micrographs revealed that P. sulphurascens hyphae colonize root surfaces and initiate the penetration of root epidermal tissues by developing appressoria within 2 d postinoculation (dpi). During early colonization, intra- and intercellular fungal hyphae were detected. They efficiently disintegrate cellular components of the host including cell walls and membranes. P. sulphurascens hyphae penetrate host cell walls by forming narrow hyphal tips and a variety of haustoria-like structures which may play important roles in pathogenic interactions. Ovomucoid-WGA (wheat germ agglutinin) conjugated gold particles (10 nm) confirmed the occurrence and location of P. sulphurascens hyphae, while four specific host pathogenesis-related (PR) protein antibodies conjugated with protein A-gold complex (20 nm) showed the localization and abundance of these PR proteins in infected root tissues. A thaumatin-like protein and an endochitinase-like protein were both strongly evident and localized in host cell membranes. A DF-PR10 protein was localized in the cell walls and cytoplasm of host cells while an antimicrobial peptide occurred in host cell walls. A close association of some PR proteins with P. sulphurascens hyphae suggests their potential antifungal activities in DF roots.

Host-Pathogen Interactions in Douglas-Fir Seedlings Infected by Phellinus sulphurascens

ABSTRACT Several aspects of the host-pathogen interaction between Douglas-fir (Pseudotsuga menziesii) and the fungal pathogen Phellinus sulphurascens were investigated in an in vitro inoculation system using young seedlings and fungal mycelia. Light microscopy confirmed that P. sulphurascens mycelia can successfully penetrate host epidermal cells within 3 days postinoculation (dpi). Extensive fungal colonization and cortical cell decay occurred within 14 dpi. Western immunoblot studies showed significant upregulation (five to sixfold) of four specific pathogenesis-related (PR) proteins in infected roots. These proteins were a Douglas-fir thaumatin-like protein (PmTLP), an endochitinase protein (ECP), a Douglas-fir PR10 (DF-PR10) protein (PsemI), and a 10.6-kDa antimicrobial peptide (PmAMP1). The highest accumulation of PmTLP and PmAMP1 occurred at 12 dpi, whereas accumulations of the ECP and DF-PR10 proteins peaked at 7 dpi. For both inoculated and control Douglas-fir seedlings, only one of the four PR proteins, PmAMP1, was clearly detectable in needles. Immunolocalization experiments using fluorescein isothiocyanate-conjugated secondary antibodies confirmed accumulation of all four PR proteins mainly in and around cell walls of root cortical tissues. Overall, the highest immunofluorescence was observed in infected roots at 12 dpi, whereas labeling in control roots was negligible at all sample times. The ECP produced the highest fluorescence; the DF-PR10 the lowest. Upregulation and localization of these PR proteins in cortical tissues of inoculated roots suggest that they play a defensive role in response to infection by P. sulphurascens. This in vitro inoculation system will facilitate further proteomic and genomic studies of this important pathosystem.

Insect feeding-induced differential expression of Beta vulgaris root genes and their regulation by defense-associated signals

Root responses to insect pests are an area of plant defense research that lacks much information. We have identified more than 150 sugar beet root ESTs enriched for genes responding to sugar beet root maggot feeding from both moderately resistant, F1016, and susceptible, F1010, genotypes using suppressive subtractive hybridization. The largest number of identified F1016 genes grouped into the defense/stress response (28%) and secondary metabolism (10%) categories with a polyphenol oxidase gene, from F1016, identified most often from the subtractive libraries. The differential expression of the root ESTs was confirmed with RT-PCR. The ESTs were further characterized using macroarray-generated expression profiles from F1016 sugar beet roots following mechanical wounding and treatment of roots with the signaling molecules methyl jasmonate, salicylic acid and ethylene. Of the examined root ESTs, 20, 17 and 11% were regulated by methyl jasmonate, salicylic acid and ethylene, respectively, suggesting these signaling pathways are involved in sugar beet root defense responses to insects. Identification of these sugar beet root ESTs provides knowledge in the field of plant root defense and will lead to the development of novel control strategies for control of the sugar beet root maggot.

Anatomical and chemical defenses of conifer bark against bark beetles and other pests

Conifers are long-lived organisms, and part of their success is due to their potent defense mechanisms. This review focuses on bark defenses, a front line against organisms trying to reach the nutrient-rich phloem. A major breach of the bark can lead to tree death, as evidenced by the millions of trees killed every year by specialized bark-invading insects. Different defense strategies have arisen in conifer lineages, but the general strategy is one of overlapping constitutive mechanical and chemical defenses overlaid with the capacity to up-regulate additional defenses. The defense strategy incorporates a graded response from 'repel', through 'defend' and 'kill', to 'compartmentalize', depending upon the advance of the invading organism. Using a combination of toxic and polymer chemistry, anatomical structures and their placement, and inducible defenses, conifers have evolved bark defense mechanisms that work against a variety of pests. However, these can be overcome by strategies including aggregation pheromones of bark beetles and introduction of virulent phytopathogens. The defense structures and chemicals in conifer bark are reviewed and questions about their coevolution with bark beetles are discussed.