Identification and analysis of differentially expressed cDNAs during nonself-competitive interaction between Phlebiopsis gigantea and Heterobasidion parviporum

Host-associated Intraspecific Phenotypic Variation in the Saprobic Fungus Phlebiopsis gigantea

Whether intraspecific phenotypic variation in saprobic fungi may be driven by the host of origin has received little attention. We addressed this issue by testing hypotheses using the model system Phlebiopsis gigantea, a wood destroying fungus associated with Picea abies and Pinus sylvestris, among others, and widely employed in practical forestry as a biological control agent. By examining approximately 60 sympatric P. gigantea isolates from both P. abies and P. sylvestris, we showed that the former grew in vitro significantly (P < 0.05) slower than the latter (average 5.56 mm/day vs. 6.84) while producing 1.8-fold significantly higher number of mitospores. An overall significant trade-off between these two phenotypic traits was detected, in particular for isolates originating from P. abies. Comparative inoculation experiments of a subsample of isolates and the assessment of mycelial growth in logs of both hosts allowed to reject the hypothesis that isolates are equally fit in terms of growth rate in wood of both hosts regardless of the host of origin. Tree models revealed that the growth rate of isolates was associated not only with the wood species in which the isolates were inoculated (P < 0.001), P. sylvestris being more rapidly colonized than P. abies, but also with the host of origin of isolates (P < 0.001). Results showed that P. gigantea isolates originating from different hosts differ phenotypically in terms of some key phenotypic traits demonstrating that a host-driven intraspecific phenotypic variation may occur in saprobic fungi.

Cysteine-Rich Hydrophobin Gene Family: Genome Wide Analysis, Phylogeny and Transcript Profiling in Cordyceps militaris

Hydrophobins are a family of small secreted proteins found exclusively in fungi, and they play various roles in the life cycle. In the present study, genome wide analysis and transcript profiling of the hydrophobin family in Cordyceps militaris, a well-known edible and medicinal mushroom, were studied. The distribution of hydrophobins in ascomycetes with different lifestyles showed that pathogenic fungi had significantly more hydrophobins than saprotrophic fungi, and class II members accounted for the majority. Phylogenetic analysis of hydrophobin proteins from the species of Cordyceps s.l. indicated that there was more variability among the class II members than class I. Only a few hydrophobin-encoding genes evolved by duplication in Cordyceps s.l., which was inconsistent with the important role of gene duplication in basidiomycetes. Different transcript patterns of four hydrophobin-encoding genes during the life cycle indicated the possible different functions for each. The transcripts of Cmhyd2, 3 and 4 can respond to light and were related with the photoreceptors. CmQHYD, with four hydrophobin II domains, was first found in C. militaris, and multi-domain hydrophobins were only distributed in the species of Cordycipitaceae and Clavicipitaceae. These results could be helpful for further function research of hydrophobins and could provide valuable information for the evolution of hydrophobins.

Genome sequencing of Rigidoporus microporus provides insights on genes important for wood decay, latex tolerance and interspecific fungal interactions

Fungal plant pathogens remain a serious threat to the sustainable agriculture and forestry, despite the extensive efforts undertaken to control their spread. White root rot disease is threatening rubber tree (Hevea brasiliensis) plantations throughout South and Southeast Asia and Western Africa, causing tree mortality and severe yield losses. Here, we report the complete genome sequence of the basidiomycete fungus Rigidoporus microporus, a causative agent of the disease. Our phylogenetic analysis confirmed the position of R. microporus among the members of Hymenochaetales, an understudied group of basidiomycetes. Our analysis further identified pathogen's genes with a predicted role in the decay of plant cell wall polymers, in the utilization of latex components and in interspecific interactions between the pathogen and other fungi. We also detected putative horizontal gene transfer events in the genome of R. microporus. The reported first genome sequence of a tropical rubber tree pathogen R. microporus should contribute to the better understanding of how the fungus is able to facilitate wood decay and nutrient cycling as well as tolerate latex and utilize resinous extractives.

The Conifer Root and Stem Rot Pathogen (Heterobasidion parviporum): Effectome Analysis and Roles in Interspecific Fungal Interactions

Heterobasidion parviporum Niemelä & Korhonen is an economically important basidiomycete, causing root and stem rot disease of Norway spruce (Picea abies (L.) Karst) in Northern Europe. The H. parviporum genome encodes numerous small secreted proteins, which might be of importance for interacting with mycorrhiza symbionts, endophytes, and other saprotrophs. We hypothesized that small secreted proteins from H. parviporum (HpSSPs) are involved in interspecific fungal interaction. To identify HpSSP-coding genes potentially involved, we screened the H. parviporum effectome and compared their transcriptomic profiles during fungal development and in planta tree infection. We further conducted phylogenetic analysis, and identified a subset of hypothetical proteins with nonpredicted domain or unknown function as HpSSPs candidates for further characterization. The HpSSPs candidates were selected based on high-quality sequence, cysteine residue frequency, protein size, and in planta expression. We subsequently explored their roles during in vitro interaction in paired cultures of H. parviporum with ectomycorrhizal Cortinarius gentilis, endophytic Phialocephala sphaeroides, saprotrophs (Mycena sp., Phlebiopsis gigantea, and Phanerochaete chrysosporium), respectively. The transcriptomic profile revealed that a large proportion of effector candidates was either barely expressed or highly expressed under all growth conditions. In vitro dual-culture test showed that P. sphaeroides and C. gentilis were overgrown by H. parviporum. The barrage zone formation or no physical contact observed in paired cultures with the saprotrophs suggest they had either combative interaction or antibiosis effect with H. parviporum. Several HpSSPs individuals were up- or downregulated during the nonself interactions. The results of HpSSPs gene expression patterns provide additional insights into the diverse roles of SSPs in tree infection and interspecific fungal interactions.

Secondary Metabolites from the Root Rot Biocontrol Fungus Phlebiopsis gigantea

Three cyclopentanoids (phlebiopsin A⁻C), one glycosylated p-terphenyl (methyl-terfestatin A), and o-orsellinaldehyde were isolated from the biocontrol fungus Phlebiopsis gigantea, and their structures were elucidated by 1D and 2D NMR spectroscopic analysis, as well as by LC-HRMS. The biological activity of the compounds against the root rot fungus Heterobasidion occidentale, as well as against Fusarium oxysporum and Penicillium canescens, was also investigated, but only o-orsellinaldehyde was found to have any antifungal activity in the concentration range tested.

Fungal wars: The underlying molecular repertoires of combating mycelia

Non-self contact between fungi elicits strong morphological and biochemical reactions in the mycelia of interacting species. Although these reactions appear to be species- and interaction-specific, some responses such as pigmentation, increased secretion of phenol-oxidases, barrage formation and sealing of the mycelia front are common responses in most interactions. Hence, some species recruit similar molecular machineries in response to non-self. Increasing number of fully sequenced and annotated fungal genomes and advances in genome-wide and global proteome analytical tools now allow researchers to use techniques such as RNA sequencing, micro and macroarray analysis, 2-dimensional protein gel profiling, and differential display of mRNA to probe the underlying molecular mechanisms of combative mycelial interactions. This review provides an overview of the genes and proteins found to be differentially expressed in conflicting fungal mycelia by the use of 'omics' tools. Connections between observed gene and protein repertoires of competing mycelia and the attendant morphological and biochemical changes are presented.

CYPome of the conifer pathogen Heterobasidion irregulare: Inventory, phylogeny, and transcriptional analysis of the response to biocontrol

The molecular mechanisms underlying the interaction of the pathogen, Heterobasidion annosum s.l., the conifer tree and the biocontrol fungus, Phlebiopsis gigantea have not been fully elucidated. Members of the cytochrome P450 (CYP) protein family may contribute to the detoxification of components of chemical defence of conifer trees by H. annosum during infection. Additionally, they may also be involved in the interaction between H. annosum and P. gigantea. A genome-wide analysis of CYPs in Heterobasidion irregulare was carried out alongside gene expression studies. According to the Standardized CYP Nomenclature criteria, the H. irregulare genome has 121 CYP genes and 17 CYP pseudogenes classified into 11 clans, 35 families, and 64 subfamilies. Tandem CYP arrays originating from gene duplications and belonging to the same family and subfamily were found. Phylogenetic analysis showed that all the families of H. irregulare CYPs were monophyletic groups except for the family CYP5144. Microarray analysis revealed the transcriptional pattern for 130 transcripts of CYP-encoding genes during growth on culture filtrate produced by P. gigantea. The high level of P450 gene diversity identified in this study could result from extensive gene duplications presumably caused by the high metabolic demands of H. irregulare in its ecological niches.

John F, Glasner J, Sabat G, Splinter BonDurant S, Syed K, Yadav J, Mgbeahuruike AC, Kovalchuk A, Asiegbu FO, Lackner G, Hoffmeister D, Rencoret J, Gutiérrez A, Sun H, Lindquist E, Barry K, Riley R, Grigoriev IV, Henrissat B, Kües U, Berka RM, Martínez AT, Covert SF, Blanchette RA, Cullen D. Analysis of the Phlebiopsis gigantea genome, transcriptome and secretome provides insight into its pioneer colonization strategies of wood

Collectively classified as white-rot fungi, certain basidiomycetes efficiently degrade the major structural polymers of wood cell walls. A small subset of these Agaricomycetes, exemplified by Phlebiopsis gigantea, is capable of colonizing freshly exposed conifer sapwood despite its high content of extractives, which retards the establishment of other fungal species. The mechanism(s) by which P. gigantea tolerates and metabolizes resinous compounds have not been explored. Here, we report the annotated P. gigantea genome and compare profiles of its transcriptome and secretome when cultured on fresh-cut versus solvent-extracted loblolly pine wood. The P. gigantea genome contains a conventional repertoire of hydrolase genes involved in cellulose/hemicellulose degradation, whose patterns of expression were relatively unperturbed by the absence of extractives. The expression of genes typically ascribed to lignin degradation was also largely unaffected. In contrast, genes likely involved in the transformation and detoxification of wood extractives were highly induced in its presence. Their products included an ABC transporter, lipases, cytochrome P450s, glutathione S-transferase and aldehyde dehydrogenase. Other regulated genes of unknown function and several constitutively expressed genes are also likely involved in P. gigantea's extractives metabolism. These results contribute to our fundamental understanding of pioneer colonization of conifer wood and provide insight into the diverse chemistries employed by fungi in carbon cycling processes.

The wood decay fungus Phlebiopsis gigantea degrades all components of plant cell walls and is uniquely able to rapidly colonize freshly exposed conifer sapwood. However, mechanisms underlying its conversion of lignocellulose and resinous extractives have not been explored. We report here analyses of the genetic repertoire, transcriptome and secretome of P. gigantea. Numerous highly expressed hydrolases, together with lytic polysaccharide monooxygenases were implicated in P. gigantea's attack on cellulose, and an array of ligninolytic peroxidases and auxiliary enzymes were also identified. Comparisons of woody substrates with and without extractives revealed differentially expressed genes predicted to be involved in the transformation of resin. These expression patterns are likely key to the pioneer colonization of conifers by P. gigantea.

Gene expression associated with intersterility in Heterobasidion

Intersterility (IS) is thought to prevent mating compatibility between homokaryons that belong to different species. Although IS in Heterobasidion is regulated by the genes located at the IS loci, it is not yet known how the IS genes influence sexual compatibility and heterokaryon formation. To increase our understanding of the molecular events underlying IS, we studied mRNA abundance changes during IS compatible and incompatible interactions over time. The clustering of the transcripts into expression profiles, followed by the application of Gene Ontology (GO) enrichment pathway analysis of each of the clusters, allowed inference of biological processes participating in IS. These analyses identified events involved in mating and sexual development (i.e., linked with IS compatibility), which included processes associated with cell-cell adhesion and recognition, cell cycle control and signal transduction. We also identified events potentially involved in overriding mating between individuals belonging to different species (i.e., linked with IS incompatibility), which included reactive oxygen species (ROS) production, responses to stress (especially to oxidative stress), signal transduction and metabolic biosynthesis. Our findings thus enabled detection and characterization of gene expression changes associated with IS in Heterobasidion, as well as identification of important processes and pathways associated with this phenomenon. Overall, the results of this study increase current knowledge regarding the molecular mechanisms underpinning IS in Heterobasidion and allowed for the establishment of a vital baseline for further studies.

Evolutionary analysis of hydrophobin gene family in two wood-degrading basidiomycetes, Phlebia brevispora and Heterobasidion annosum s.l

Background

Hydrophobins are small secreted cysteine-rich proteins that play diverse roles during different phases of fungal life cycle. In basidiomycetes, hydrophobin-encoding genes often form large multigene families with up to 40 members. The evolutionary forces driving hydrophobin gene expansion and diversification in basidiomycetes are poorly understood. The functional roles of individual genes within such gene families also remain unclear. The relationship between the hydrophobin gene number, the genome size and the lifestyle of respective fungal species has not yet been thoroughly investigated. Here, we present results of our survey of hydrophobin gene families in two species of wood-degrading basidiomycetes, Phlebia brevispora and Heterobasidion annosum s.l. We have also investigated the regulatory pattern of hydrophobin-encoding genes from H. annosum s.s. during saprotrophic growth on pine wood as well as on culture filtrate from Phlebiopsis gigantea using micro-arrays. These data are supplemented by results of the protein structure modeling for a representative set of hydrophobins.

Results

We have identified hydrophobin genes from the genomes of two wood-degrading species of basidiomycetes, Heterobasidion irregulare, representing one of the microspecies within the aggregate H. annosum s.l., and Phlebia brevispora. Although a high number of hydrophobin-encoding genes were observed in H. irregulare (16 copies), a remarkable expansion of these genes was recorded in P. brevispora (26 copies). A significant expansion of hydrophobin-encoding genes in other analyzed basidiomycetes was also documented (1–40 copies), whereas contraction through gene loss was observed among the analyzed ascomycetes (1–11 copies). Our phylogenetic analysis confirmed the important role of gene duplication events in the evolution of hydrophobins in basidiomycetes. Increased number of hydrophobin-encoding genes appears to have been linked to the species’ ecological strategy, with the non-pathogenic fungi having increased numbers of hydrophobins compared with their pathogenic counterparts. However, there was no significant relationship between the number of hydrophobin-encoding genes and genome size. Furthermore, our results revealed significant differences in the expression levels of the 16 H. annosum s.s. hydrophobin-encoding genes which suggest possible differences in their regulatory patterns.

Conclusions

A considerable expansion of the hydrophobin-encoding genes in basidiomycetes has been observed. The distribution and number of hydrophobin-encoding genes in the analyzed species may be connected to their ecological preferences. Results of our analysis also have shown that H. annosum s.l. hydrophobin-encoding genes may be under positive selection. Our gene expression analysis revealed differential expression of H. annosum s.s. hydrophobin genes under different growth conditions, indicating their possible functional diversification.

Expression analysis of the impact of culture filtrates from the biocontrol agent, Phlebiopsis gigantea on the conifer pathogen, Heterobasidion annosum s.s. Transcriptome

Phlebiopsis gigantea has been routinely used as the biological control agent for the conifer pathogen Heterobasidion annosum sensu lato, but the actual mechanism for the biocontrol process is not known. To investigate the effect of secreted molecules from culture filtrate produced by P. gigantea on the gene expression profile of H. annosum s.s., microarray analysis was used. Analysis of the differentially expressed genes led to the identification of genes with diverse functions. A major proportion of the up- and downregulated genes were either uncharacterized or genes whose functions were not known. A number of genes coding for proteins involved in metabolism, transport, and signal transduction were differentially downregulated; comparatively lower number of such genes were upregulated. Some genes involved in transport (polyamine transporters, 2573-fold, P = 0.002) and metabolism (endoglucanase, 622.5-fold, P = 0.002, cytochrome P450, 133.2-fold, P = 0.05) showed high transcript fold changes and were statistically significantly upregulated. Genes encoding defense-related proteins such as hydrophobins were either downregulated or expressed at relatively low levels. Further analysis of the effect of the culture filtrate on glucose metabolism showed downregulation of some key enzymes at the early stage of the glycolytic pathway while some genes were upregulated at the later stage of the pathway. A subset of the genes were selected and used to validate the micro-array result by quantitative real time polymerase chain reaction (qPCR) method. Generally, the high transcript levels of genes encoding several biochemically important genes (protein kinases, major facilitator superfamily polyamine transporters, endoglucanase, cytochrome P450, endoglucanase) suggests their potential functional relevance in signal perception, stress tolerance, cell defenses, and detoxification of toxic molecules during competitive interaction. These results have provided further insights into possible molecular and genetic factors underlying the response of H. annosum to metabolites from P. gigantea during interspecific interaction.

A 2nd generation linkage map of Heterobasidion annosum s.l. based on in silico anchoring of AFLP markers

In this study, we present a 2^nd generation genetic linkage map of a cross between the North American species Heterobasidion irregulare and H. occidentale, based on the alignment of the previously published 1^st generation map to the parental genomes. We anchored 216 of the original 308 AFLP markers to their respective restriction sites using an in silico-approach. The map resolution was improved by adding 146 sequence-tagged microsatellite markers and 39 sequenced gene markers. The new markers confirmed the positions of the anchored AFLP markers, fused the original 39 linkage groups together into 17, and fully expanded 12 of these to single groups covering entire chromosomes. Map coverage of the genome increased from 55.3% to 92.8%, with 96.3% of 430 markers collinearly aligned with the genome sequence. The anchored map also improved the H. irregulare assembly considerably. It identified several errors in scaffold arrangements and assisted in reducing the total number of major scaffolds from 18 to 15. This denser, more comprehensive map allowed sequence-based mapping of three intersterility loci and one mating type locus. This demonstrates the possibility to utilize an in silico procedure to convert anonymous markers into sequence-tagged ones, as well as the power of a sequence-anchored linkage map and its usefulness in the assembly of a whole genome sequence.

Differential expression of two hydrophobin genes (Pgh1 and Pgh2) from the biological control agent Phlebiopsis gigantea

Phlebiopsis gigantea has been widely used as the biocontrol fungus against the root and butt rot disease of conifers caused by Heterobasidion annosum. We investigated the regulation of two hydrophobin genes (Pgh1 and Pgh2) in strong and weak antagonistic isolates of the biological control agent P. gigantea under diverse substrate conditions. Transcript abundance of Pgh1 was higher in single cultures of strong performing isolates than in the weak performing isolates at the early and late stages of the fungal growth (P =0.05). Higher fold transcript changes of Pgh1 and Pgh2 were observed in the strong performing isolates at the early stage of the antagonistic interaction on modified Norkrans sawdust agar medium compared to the weak performing isolates. Higher transcript abundance of the two genes was also observed during growth in submerged compared to surface agar cultures (P<0.003 and P=0.0001 for Pgh1 and Pgh2, respectively). No correlation between antagonistic ability and sequence characteristics of either gene was found but a significant correlation was found between some strong performing isolates and the expression of Pgh1. Regulatory patterns of both Pgh1 and Pgh2 suggest a role during early stages of interaction between the two fungi and their potential roles in the biological control process is discussed.

The mycelial response of the white-rot fungus, Schizophyllum commune to the biocontrol agent, Trichoderma viride

In this study, agar plate interaction between Schizophyllum commune and Trichoderma viride was investigated to characterise the physiological responses occurring during interspecific mycelial combat. The metabolite profiles and morphological changes in both fungi paired on agar were studied relative to the modulation of phenoloxidase activity in S. commune. The calcium ionophore A23187 was incorporated in self-paired cultures of S. commune to explore possible involvement of calcium influx in the response of S. commune to T. viride. The levels of lipid peroxides and protein carbonyls in the confronted mycelia of S. commune were also measured. Contact with T. viride induced pigmentation and cell wall hydrolysis in S. commune with concomitant increase in phenoloxidase activity, rise in the levels of oxidative stress indicators and increased levels of phenolic compounds, antioxidant γ-amino butyric acid, and pyridoxine and osmo-protective sugar alcohols. Calcium ionophore mimicked the pigmentation in the T. viride-confronted mycelia of S. commune, implicating calcium influx in the response to T. viride. The changes in S. commune are indicative of targeted responses to osmotic and oxidative stresses and phenoloxidase-mediated detoxification of noxious compounds in the contact interface with T. viride, which may confer resistance in natural environments.

Response of living tissues of Pinus sylvestris to the saprotrophic biocontrol fungus Phlebiopsis gigantea

The saprotrophic fungus Phlebiopsis gigantea has been used for several years as a biocontrol agent against the conifer pathogen Heterobasidion annosum. Although the effectiveness of P. gigantea in biocontrol has been shown empirically, the long-term effect on living conifer trees as well as the mechanism underlying its antagonistic activity is still unknown. An additional concern is the potential of P. gigantea to acquire a necrotrophic habit through adaptation to living wood tissues. By using a combination of histochemical, molecular and transcript profiling (454 sequencing), we investigated under in vitro conditions the necrotrophic capability of P. gigantea and induced localized resistance as a mechanism for its biocontrol action. Pinus sylvestris seedlings (10 years old) were challenged on the xylem surface with P. gigantea or H. annosum. Both fungi provoked strong necrotic lesions, but after prolonged incubation, P. gigantea lesions shrank and ceased to expand further. Tree seedlings pre-treated with P. gigantea further restricted H. annosum-induced necrosis and had more lignified cells. The 454 sequencing revealed elevated transcript levels of genes important for lignification, cell death regulation and jasmonic acid signalling. The results suggest that induced localized resistance is a contributory factor for the biocontrol efficacy of P. gigantea, and it has a limited necrotrophic capability compared with H. annosum.

WS-5995 B, an antifungal agent inducing differential gene expression in the conifer pathogen Heterobasidion annosum but not in Heterobasidion abietinum

The mycorrhization helper bacterium Streptomyces sp. AcH 505 inhibits Norway spruce root infection and colonisation by the root and butt rot fungus Heterobasidion annosum 005 but not by the congeneric strain Heterobasidion abietinum 331 because of higher sensitivity of H. annosum 005 towards the AcH 505-derived naphthoquinone antibiotic WS-5995 B. Differences in antibiotic sensitivity between two isolates belonging to two species, H. annosum 005 and H. abietinum 331, were investigated by comparative gene expression analysis using macroarrays and quantitative RT-PCR after WS-5995 B, structurally related mollisin and unrelated cycloheximide application. Treatment with 25 microM WS-5995 B for 2 h resulted in a significant up-regulation of expression of inosine-5'-monophosphate dehydrogenase, phosphoglucomutase and GTPase genes, while the expression of genes encoding for thioredoxin and glutathione dependent formaldehyde dehydrogenase was down-regulated in the sensitive fungal strain. No differential expression in the tolerant strain was detected. Application of WS-5995 B at higher concentrations over a time course experiment revealed that H. annosum 005 and H. abietinum 331 responded differently to WS-5995 B. The fungal gene expression levels depended on both the concentration of WS-5995 B and the duration of its application. The WS-5995 B-unrelated cycloheximide caused highly specific changes in patterns of gene expression. Our findings indicate considerable variations in response to bacterial metabolites by the isolates of the conifer pathogen.

Use of a breeding approach for improving biocontrol efficacy of Phlebiopsis gigantea strains against Heterobasidion infection of Norway spruce stumps

Sixty-four wild heterokaryotic isolates of Phlebiopsis gigantea were analysed for asexual spore production, growth rate and competitive ability against Heterobasidion in vitro, as well as growth rate in Norway spruce wood. These P. gigantea traits were considered important for controlling infection of Norway spruce stumps by spores of Heterobasidion spp. Ten most promising P. gigantea isolates were crossed with each other and 172 F(1) progeny heterokaryons were analysed for the above-mentioned traits. Thirteen most promising progeny heterokaryons were selected and their biocontrol ability against infection by Heterobasidion was compared with the parental isolates in stem pieces of Norway spruce. The results indicated that the progeny strains had generally better traits and control efficacy than the parental strains. The genetic effects accounted for a part of the variations between progeny and parental strains. This further suggests that there is a potential to improve the biocontrol properties of P. gigantea through breeding.

Molecular cloning and characterization of a short type peptidoglycan recognition protein (CfPGRP-S1) cDNA from Zhikong scallop Chlamys farreri

Peptidoglycan recognition protein (PGRP) specifically binds to peptidoglycan and plays a crucial role in the innate immune responses as a pattern recognition receptor (PRR). The cDNA of a short type PGRP was cloned from scallop Chlamys farreri (named CfPGRP-S1) by homology cloning with degenerate primers, and confirmed by virtual Northern blots. The full length of CfPGRP-S1 cDNA was 1073 bp in length, including a 5' untranslated region (UTR) of 59 bp, a 3' UTR of 255 bp, and an open reading frame (ORF) of 759 bp encoding a polypeptide of 252 amino acids with an estimated molecular mass of 27.88 kDa and a predicted isoelectric point of 8.69. BLAST analysis revealed that CfPGRP-S1 shared high identities with other known PGRPs. A conserved PGRP domain and three zinc-binding sites were present at its C-terminus. The temporal expression of CfPGRP-S1 gene in healthy, Vibrio anguillarum-challenged and Micrococcus lysodeikticus-challenged scallops was measured by RT-PCR analysis. The expression of CfPGRP-S1 was upregulated initially in the first 12 h or 24 h either by M. lysodeikticus or V. anguillarum challenge and reached the maximum level at 24 h or 36 h, then dropped progressively, and recovered to the original level as the stimulation decreased at 72 h. There was no significant difference between V. anguillarum and M. lysodeikticus challenge. The results indicated that the CfPGRP-S1 was a constitutive and inducible acute-phase protein which was involved in the immune response against bacterial infection.