cDNA cloning of a sorghum pathogenesis-related protein (PR-10) and differential expression of defense-related genes following inoculation with Cochliobolus heterostrophus or Colletotrichum sublineolum

ANTHRACNOSE RESISTANCE GENE2 confers fungal resistance in sorghum

Sorghum is an important food and feed crop globally; its production is hampered by anthracnose disease caused by the fungal pathogen Colletotrichum sublineola (Cs). Here, we report identification and characterization of ANTHRACNOSE RESISTANCE GENE 2 (ARG2) encoding a nucleotide-binding leucine-rich repeat (NLR) protein that confers race-specific resistance to Cs strains. ARG2 is one of a cluster of several NLR genes initially identified in the sorghum differential line SC328C that is resistant to some Cs strains. This cluster shows structural and copy number variations in different sorghum genotypes. Different sorghum lines carrying independent ARG2 alleles provided the genetic validation for the identity of the ARG2 gene. ARG2 expression is induced by Cs, and chitin induces ARG2 expression in resistant but not in susceptible lines. ARG2-mediated resistance is accompanied by higher expression of defense and secondary metabolite genes at early stages of infection, and anthocyanin and zeatin metabolisms are upregulated in resistant plants. Interestingly, ARG2 localizes to the plasma membrane when transiently expressed in Nicotiana benthamiana. Importantly, ARG2 plants produced higher shoot dry matter than near-isogenic lines carrying the susceptible allele suggesting an absence of an ARG2 associated growth trade-off. Furthermore, ARG2-mediated resistance is stable at a wide range of temperatures. Our observations open avenues for resistance breeding and for dissecting mechanisms of resistance.

Comparative transcriptomics unravels new genes imparting scab resistance in apple (Malus x domestica Borkh.)

Apple scab is caused by an ascomycete fungus, Venturia inaequalis (Cke.) Wint., which is one of the most severe disease of apple (Malus × Domestica Borkh.) worldwide. The disease results in 30-40% fruit loss annually and even complete loss in some places. Owing to the evolving susceptibility of resistant apple genotypes harboring R-genes to new variants of V. inaequalis, a comparative transcriptome analysis using Illumina (HiSeq) platform of three scab-resistant (Florina, Prima, and White Dotted Red) and three susceptible (Ambri, Vista Bella, and Red Delicious) apple genotypes was carried out to mine new scab resistance genes. The study led to the identification of 822 differentially expressed genes in the tested scab-resistant and scab-susceptible apple genotypes. The most upregulated genes uniformly expressed in resistant varieties compared to susceptible ones were those coding for 17.3 kDa class II heat shock protein-like, chaperone protein ClpB1, glutathione S-transferase L3-like protein, B3 domain-containing protein At3g18960-like, transcription factor bHLH7, zinc finger MYM-type protein 1-like, and nine uncharacterized proteins, besides three lncRNAs. The genes that were downregulated in susceptible and upregulated in resistant cultivars were those coding for non-specific lipid transfer protein GPI-anchored 1, rust resistance kinase Lr10-like, disease resistance protein RPS6-like, and many uncharacterized proteins. DESeq2 analysis too revealed 20 DEGs that were upregulated in scab-resistant cultivars. Furthermore, a total of 361 genes were significantly upregulated in scab-susceptible variety, while 461 were found downregulated (P value < 0.05 and Log2 (FC) > 1). The differentially expressed genes (DEGs) were related to various pathways, i.e., metabolic, protein processing, biosynthesis of secondary metabolites, plant hormone signal transduction, autophagy, ubiquitin-mediated proteolysis, plant-pathogen interaction, lipid metabolism, and protein modification pathways. Real-time expression of a set of selected twelve DEGs further validated the results obtained from RNA-seq. Overall, these findings lay the foundation for investigating the genetic basis of apple scab resistance and defense pathways that might have a plausible role in governing scab resistance in apple against V. inaequalis.

Two pathogenesis-related proteins interact with leucine-rich repeat proteins to promote Alternaria leaf spot resistance in apple

Alternaria leaf spot in apple (Malus x domestica), caused by the fungal pathogen Alternaria alternata f. sp. mali (also called A. mali), is a devastating disease resulting in substantial economic losses. We previously established that the resistance (R) protein MdRNL2, containing a coiled-coil, nucleotide-binding, and leucine-rich repeat (CC_R-NB-LRR) domain, interacts with another CC_R-NB-LRR protein, MdRNL6, to form a MdRNL2-MdRNL6 complex that confers resistance to A. mali. Here, to investigate the function of the MdRNL2-MdRNL6 complex, we identified two novel pathogenesis-related (PR) proteins, MdPR10-1 and MdPR10-2, that interact with MdRNL2. Yeast two-hybrid (Y2H) assays and bimolecular fluorescence complementation (BiFC) assays confirmed that MdPR10-1 and MdPR10-2 interact with MdRNL2 and MdRNL6 at the leucine-rich repeat domain. Transient expression assays demonstrated that accumulation of MdPR10-1 and MdPR10-2 enhanced the resistance of apple to four strains of A. mali that we tested: ALT1, GBYB2, BXSB5, and BXSB7. In vitro antifungal activity assays demonstrated that both the proteins contribute to Alternaria leaf spot resistance by inhibiting fungal growth. Our data provide evidence for a novel regulatory mechanism in which MdRNL2 and MdRNL6 interact with MdPR10-1 and MdPR10-2 to inhibit fungal growth, thereby contributing to Alternaria leaf spot resistance in apple. The identification of these two novel PR proteins will facilitate breeding for fungal disease resistance in apple.

Variation in Gene Expression between Two Sorghum bicolor Lines Differing in Innate Immunity Response

Microbe associated molecular pattern (MAMPs) triggered immunity (MTI) is a key component of the plant innate immunity response to microbial recognition. However, most of our current knowledge of MTI comes from model plants (i.e., Arabidopsis thaliana) with comparatively less work done using crop plants. In this work, we studied the MAMP triggered oxidative burst (ROS) and the transcriptional response in two Sorghum bicolor genotypes, BTx623 and SC155-14E. SC155-14E is a line that shows high anthracnose resistance and the line BTx623 is susceptible to anthracnose. Our results revealed a clear variation in gene expression and ROS in response to either flagellin (flg22) or chitin elicitation between the two lines. While the transcriptional response to each MAMP and in each line was unique there was a considerable degree of overlap, and we were able to define a core set of genes associated with the sorghum MAMP transcriptional response. The GO term and KEGG pathway enrichment analysis discovered more immunity and pathogen resistance related DEGs in MAMP treated SC155-14E samples than in BTx623 with the same treatment. The results provide a baseline for future studies to investigate innate immunity pathways in sorghum, including efforts to enhance disease resistance.

Phenotypic, Phytochemical, and Transcriptomic Analysis of Black Sorghum (Sorghum bicolor L.) Pericarp in Response to Light Quality

Black sorghum [Sorghum bicolor (L.) Moench] is characterized by the black appearance of the pericarp and production of 3-deoxyanthocyanidins (3-DOA), which are valued for their cytotoxicity to cancer cells and as natural food colorants and antioxidant additives. The black pericarp phenotype is not fully penetrant in all environments, which implicates the light spectrum and/or photoperiod as the critical factor for trait expression. In this study, black- or red-pericarp genotypes were grown under regimes of visible light, visible light supplemented with UVA or supplemented with UVA plus UVB (or dark control). Pericarp 3-DOAs and pericarp pigmentation were maximized in the black genotype exposed to a light regime supplemented with UVB. Changes in gene expression during black pericarp development revealed that ultraviolet light activates genes related to plant defense, reactive oxygen species, and secondary metabolism, suggesting that 3-DOA accumulation is associated with activation of flavonoid biosynthesis and several overlapping defense and stress signaling pathways.

Parallel Transcriptional Regulation of Artemisinin and Flavonoid Biosynthesis

Plants regulate the synthesis of specialized compounds through the actions of individual transcription factors (TFs) or sets of TFs. One such compound, artemisinin from Artemisia annua, is widely used as a pharmacological product in the first-line treatment of malaria. However, the emergence of resistance to artemisinin in Plasmodium species, as well as its low production rates, have required innovative treatments such as exploiting the synergistic effects of flavonoids with artemisinin. We overview current knowledge about flavonoid and artemisinin transcriptional regulation in A. annua, and review the dual action of TFs and structural genes that can regulate both pathways simultaneously. Understanding the concerted action of these TFs and their associated structural genes can guide the development of strategies to further improve flavonoid and artemisinin production.

Alternative splicing is a Sorghum bicolor defense response to fungal infection

This study provides new insights that alternative splicing participates with transcriptional control in defense responses to Colletotrichum sublineola in sorghum In eukaryotic organisms, alternative splicing (AS) is an important post-transcriptional mechanism to generate multiple transcript isoforms from a single gene. Protein variants translated from splicing isoforms may have altered molecular characteristics in signal transduction and metabolic activities. However, which transcript isoforms will be translated into proteins and the biological functions of the resulting proteoforms are yet to be identified. Sorghum is one of the five major cereal crops, but its production is severely affected by fungal diseases. For example, sorghum anthracnose caused by Colletotrichum sublineola greatly reduces grain yield and biomass production. In this study, next-generation sequencing technology was used to analyze C. sublineola-inoculated sorghum seedlings compared with mock-inoculated control. It was identified that AS regulation may be as important as traditional transcriptional control during defense responses to fungal infection. Moreover, several genes involved in flavonoid and phenylpropanoid biosynthetic pathways were found to undergo multiple AS modifications. Further analysis demonstrated that non-conventional targets of both 5'- and 3'-splice sites were alternatively used in response to C. sublineola infection. Splicing factors were also affected at both transcriptional and post-transcriptional levels. As the first transcriptome report on C. sublineola infected sorghum, our work also suggested that AS plays crucial functions in defense responses to fungal invasion.

Analysis of differential transcript expression in chickpea during compatible and incompatible interactions with Fusarium oxysporum f. sp. ciceris Race 4

The present study reports the transcriptome analysis of resistance (WR315) and susceptible (JG62) genotypes of chickpea in response to Fusarium oxysporum f. sp. ciceris (Foc) race 4 using the method of suppression subtractive hybridization. Altogether, 162 chickpea-expressed sequence tags (ESTs) were identified from two libraries and analyzed to catalog eight functional categories. These ESTs could be assembled into 18 contigs and 144 singletons with 10 contigs and 68 singletons from compatible and 8 contigs and 70 singletons from incompatible interaction. The largest category consisted of ESTs which encode for proteins related to hypothetical proteins (22.8%), followed by energy and metabolism (20.3%)-related genes, defense and cell rescue-related genes (17.9%) and signal transduction-related genes (16%). Among them, 17.1 and 18.7% were defense-related genes in compatible and incompatible interaction, respectively. These ESTs mainly includes various putative genes related to oxidative burst, pathogenesis and secondary metabolism. Induction of putative superoxide dismutase, metallothionein, 4-coumarate-CoA ligase, heat shock proteins and cysteine proteases indicated oxidative burst after infection. The ESTs belonged to various functional categories which were directly and indirectly associated with defense signaling pathways. Quantitative and semi-quantitative polymerase chain reaction exhibited differential expression of candidate genes and detected higher levels in incompatible interaction compared to compatible interaction. The present study revealed partial molecular mechanism associated with the resistance in chickpea against Foc, which is the key to design a strategy for incorporation of resistance via either biotechnological means or introgression of resistance genes.

A sugarcane pathogenesis-related protein, ScPR10, plays a positive role in defense responses under Sporisorium scitamineum, SrMV, SA, and MeJA stresses

KEY MESSAGE

A pathogenesis-related gene, ScPR10 , was isolated from sugarcane and its bio-function was characterized, demonstrating that ScPR10 was involved in plant defense responses to Sporisorium scitamineum , SrMV, SA, and MeJA stresses. Plant fungal and viral diseases are the major concerns in sugarcane industry. Many anti-fungal and antivirus components, including pathogenesis-related (PR) proteins, have been identified. The pathogenesis-related protein 10 (PR10) is the dominant group in PR families, involved in the plant defense mechanism. In this study, ScPR10 (GenBank Acc. No. KT887884), a 701-bp-length PR10 gene with a 483 bp-length open reading frame, was isolated from sugarcane. Its transient expression in the leaves of Nicotiana benthamiana indicated that the function role of ScPR10 is likely in the nucleus, and it increased the level of H2O2 accumulation in leaf cells. Moreover, ScPR10 could also enhance the resistance of N. benthamiana leaves to infection by Pseudomonas solanacearum and Fusarium solani var. coeruleum. Quantitative real-time PCR analysis revealed that ScPR10 was not constitutively expressed in sugarcane tissues due to its high expression in the buds and scant presence in root tips. In addition, the transcript of ScPR10 could be induced by a pathogenic fungus (Sporisorium scitamineum) and a virus (Sorghum mosaic virus, SrMV) in the resistant sugarcane cultivars, while it was down-regulated in the susceptible ones. After exposure to salicylic acid (SA) and methyl jasmonate (MeJA), ScPR10 peaked at 6 and 12 h, respectively. These results suggest that ScPR10 can play a positive role in sugarcane defense responses to S. scitamineum, SrMV, SA, and MeJA stresses.

A novel PR10 promoter from Erianthus arundinaceus directs high constitutive transgene expression and is enhanced upon wounding in heterologous plant systems

In genetic engineering, inducible promoters play an important role as the expression of genes driven by them can be turned on or off under situations like biotic or abiotic factors. There are few reports on inducible promoters that can be employed in the development of transgenic plants, particularly in sugarcane. In the present study, four wound inducible genes (Chitinase, PR1A, PR10 and HRGP) were selected and were amplified from Erianthus arundinaceus, a distant relative of sugarcane. In order to determine the gene that is highly induced upon wounding, RT-qPCR was performed, which showed that PR10 gene expression was instantaneous and higher upon wounding when compared to the other three genes. Using the random amplification of genomic ends technique, a 592 bp promoter sequence was obtained and in silico analysis of the upstream regulatory region revealed a 469 bp promoter and 123 bp of 5' untranslated region (UTR). Functional analyses of the promoter sequence (with and without 5' UTR) in tobacco, rice and sugarcane using β-glucuronidase (GUS) as the reporter gene revealed the constitutive and inducible nature of the PR10 promoter. Our studies have demonstrated that the PR10 promoter, though highly constitutive, was quickly induced upon wounding as well as on treatment with abscisic acid and methyl jasmonate hormones. This is the first report on the isolation and characterization of a PR10 promoter from a wild grass and is expected to have application for development of transgenic plants.

Gene expression profiling by cDNA-AFLP reveals potential candidate genes for partial resistance of 'Président Roulin' against Venturia inaequalis

Background

Scab, caused by the fungus Venturia inaequalis, is one of the most important diseases of cultivated apple. While a few scab resistance genes (R genes) governing qualitative resistance have been isolated and characterized, the biological roles of genes governing quantitative resistance, supposed to be more durable, are still unknown. This study aims to investigate the molecular mechanisms involved in the partial resistance of the old Belgian apple cultivar ‘Président Roulin’ against V. inaequalis.

Results

A global gene expression analysis was conducted in ‘Président Roulin’ (partially resistant) and in ‘Gala’ (susceptible) challenged by V. inaequalis by using the cDNA-AFLP method (cDNA-Amplified Fragment Length Polymorphism). Transcriptome analysis revealed significant modulation (up- or down-regulation) of 281 out of approximately 20,500 transcript derived fragments (TDFs) in ‘Président Roulin’ 48 hours after inoculation. Sequence annotation revealed similarities to several genes encoding for proteins belonging to the NBS-LRR and LRR-RLK classes of plant R genes and to other defense-related proteins. Differentially expressed genes were sorted into functional categories according to their gene ontology annotation and this expression signature was compared to published apple cDNA libraries by Gene Enrichment Analysis. The first comparison was made with two cDNA libraries from Malus x domestica uninfected leaves, and revealed in both libraries a signature of enhanced expression in ‘Président Roulin’ of genes involved in response to stress and photosynthesis. In the second comparison, the pathogen-responsive TDFs from the partially resistant cultivar were compared to the cDNA library from inoculated leaves of Rvi6 (HcrVf2)-transformed ‘Gala’ lines (complete disease resistance) and revealed both common physiological events, and notably differences in the regulation of defense response, the regulation of hydrolase activity, and response to DNA damage. TDFs were in silico mapped on the ‘Golden Delicious’ apple reference genome and significant co-localizations with major scab R genes, but not with quantitative trait loci (QTLs) for scab resistance nor resistance gene analogues (RGAs) were found.

Conclusions

This study highlights possible candidate genes that may play a role in the partial scab resistance mechanisms of ‘Président Roulin’ and increase our understanding of the molecular mechanisms involved in the partial resistance against apple scab.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1043) contains supplementary material, which is available to authorized users.

Red card for pathogens: phytoalexins in sorghum and maize

Cereal crop plants such as maize and sorghum are constantly being attacked by a great variety of pathogens that cause large economic losses. Plants protect themselves against pathogens by synthesizing antimicrobial compounds, which include phytoalexins. In this review we summarize the current knowledge on phytoalexins produced by sorghum (luteolinidin, apigeninidin) and maize (zealexin, kauralexin, DIMBOA and HDMBOA). For these molecules, we highlight biosynthetic pathways, known intermediates, proposed enzymes, and mechanisms of elicitation. Finally, we discuss the involvement of phytoalexins in plant resistance and their possible application in technology, medicine and agriculture. For those whose world is round we tried to set the scene in the context of a hypothetical football game in which pathogens fight with phytoalexins on the different playing fields provided by maize and sorghum.

The endoplasmic reticulum binding protein BiP displays dual function in modulating cell death events

The binding protein (BiP) has been demonstrated to participate in innate immunity and attenuate endoplasmic reticulum- and osmotic stress-induced cell death. Here, we employed transgenic plants with manipulated levels of BiP to assess whether BiP also controlled developmental and hypersensitive programmed cell death (PCD). Under normal conditions, the BiP-induced transcriptome revealed a robust down-regulation of developmental PCD genes and an up-regulation of the genes involved in hypersensitive PCD triggered by nonhost-pathogen interactions. Accordingly, the BiP-overexpressing line displayed delayed leaf senescence under normal conditions and accelerated hypersensitive response triggered by Pseudomonas syringae pv tomato in soybean (Glycine max) and tobacco (Nicotiana tabacum), as monitored by measuring hallmarks of PCD in plants. The BiP-mediated delay of leaf senescence correlated with the attenuation of N-rich protein (NRP)-mediated cell death signaling and the inhibition of the senescence-associated activation of the unfolded protein response (UPR). By contrast, under biological activation of salicylic acid (SA) signaling and hypersensitive PCD, BiP overexpression further induced NRP-mediated cell death signaling and antagonistically inhibited the UPR. Thus, the SA-mediated induction of NRP cell death signaling occurs via a pathway distinct from UPR. Our data indicate that during the hypersensitive PCD, BiP positively regulates the NRP cell death signaling through a yet undefined mechanism that is activated by SA signaling and related to ER functioning. By contrast, BiP's negative regulation of leaf senescence may be linked to its capacity to attenuate the UPR activation and NRP cell death signaling. Therefore, BiP can function either as a negative or positive modulator of PCD events.

Structural and functional aspects of PR-10 proteins

Physical, chemical and biological stress factors, such as microbial infection, upregulate the transcription levels of a number of plant genes, coding for the so-called pathogenesis-related (PR) proteins. For PR proteins of class-10 (PR-10), the biological function remains unclear, despite two decades of scientific research. PR-10 proteins have a wide distribution throughout the plant kingdom and the class members share size and secondary structure organization. Throughout the years, we and other groups have determined the structures of a number of PR-10 proteins, both in the crystalline state by X-ray diffraction and in solution by NMR spectroscopy. Despite the accumulating structural information, our understanding of PR-10 function is still limited. PR-10 proteins are rather small (~ 160 amino acids) with a fold consisting of three α helices and seven antiparallel β strands. These structural elements enclose a large hydrophobic cavity that is most probably the key to their functional relevance. Also, the outer surface of these proteins is of extreme interest, as epitopes from a PR-10 subclass cause allergic reactions in humans.

Identification and characterization of stress resistance related genes of Brassica rapa

Two biotic stress resistance related genes from the full-length cDNA library of Brassica rapa cv. Osome were identified from EST analysis and determined to be pathogenesis-related (PR) 12 Brassica defensin-like family protein (BrDLFP) and PR-10 Brassica Betv1 allergen family protein (BrBetv1AFP) after sequence analysis and homology study with other stress resistance related same family genes. In the expression analysis, both genes expressed in different organs and during all developmental growth stages in healthy plants. Expression of BrDLFP significantly increased and BrBetv1AFP gradually decreased after infection with Pectobacterium carotovorum subsp. carotovorum in Chinese cabbage. Expression of these two genes significantly changed after cold, salt, drought and ABA stress treatments. These two PR genes may therefore be involved in the plant resistance against biotic and abiotic stresses.

Two loci in sorghum with NB-LRR encoding genes confer resistance to Colletotrichum sublineolum

The aim of this work was to identify plant resistance genes to the sorghum anthracnose fungus Colletotrichum sublineolum. cDNA-AFLP transcript profiling on two contrasting sorghum genotypes inoculated with C. sublineolum generated about 3,000 informative fragments. In a final set of 126 sequenced genes, 15 were identified as biotic stress related. Seven of the plant-derived genes were selected for functional analysis using a Brome mosaic virus-based virus-induced gene silencing (VIGS) system followed by fungal inoculation and quantitative real-time PCR analysis. The candidate set comprised genes encoding resistance proteins (Cs1A, Cs2A), a lipid transfer protein (SbLTP1), a zinc finger-like transcription factor (SbZnTF1), a rice defensin-like homolog (SbDEFL1), a cell death related protein (SbCDL1), and an unknown gene harboring a casein kinase 2-like domain (SbCK2). Our results demonstrate that down-regulation of Cs1A, Cs2A, SbLTP1, SbZnF1 and SbCD1 via VIGS, significantly compromised the resistance response while milder effects were observed with SbDEFL1 and SbCK2. Expanded genome analysis revealed that Cs1A and Cs2A genes are located in two different loci on chromosome 9 closely linked with duplicated genes Cs1B and Cs2B, respectively. The nucleotide binding-leucine rich repeat (NB-LRR) encoding Cs gene sequence information is presently employed in regional breeding programs.

Identification of differentially expressed genes in a resistant versus a susceptible blueberry cultivar after infection by Colletotrichum acutatum

Anthracnose fruit rot, caused by the fungus Colletotrichum acutatum, is an important disease of blueberry worldwide. The cultivar Elliott is resistant, severely restricting fungal growth and sporulation relative to the susceptible cultivar Jersey. The objectives of this research were as follows: (i) to analyse pre-penetration events in 'Elliott' and 'Jersey' at different stages of fruit development; (ii) to identify putative defence genes in 'Elliott' fruit; and (iii) to monitor the timing of the oxidative burst in both cultivars. Light microscopy revealed no differences in the pre-penetration activities of C. acutatum on the immature fruit of both cultivars. However, at fruit ripening, conidia germinated and formed appressoria more rapidly on 'Jersey' than on 'Elliott' fruit. Using suppression subtractive hybridization, 37 differentially expressed sequence tags (ESTs) were detected in 'Elliott' versus 'Jersey' upon infection. Several of the ESTs had homology to known plant defence genes, such as a class II chitinase, pathogenesis-related protein 10 (PR10) and β-1,3-glucanase. Two putative genes involved in oxidative stress were identified: a metallothionein-like protein and monodehydroascorbate reductase. ESTs of fungal origin were also detected. Many ESTs had no homology to known genes. Using semi-quantitative and quantitative reverse transcription-polymerase chain reaction (RT-PCR), the expression of most of the candidate genes was detected earlier in 'Elliott' than in 'Jersey', some within 24 h post inoculation (hpi). Monitoring of the oxidative burst showed that the overall H(2) O(2) concentration was two to three times higher in 'Elliott' than in 'Jersey' at 24 hpi. The elucidation of the basis of resistance to C. acutatum in blueberry will facilitate the development of new anthracnose fruit rot-resistant cultivars.

A comparison of two class 10 pathogenesis-related genes from alfalfa and their activation by multiple stresses and stress-related signaling molecules

A collection of 29 pathogenesis-related 10 (PR10) genes of Medicago sativa and Medicago truncatula showed that they were almost all obtained from cDNA libraries of tissues undergoing abiotic or biotic stresses. The predicted proteins could be divided into two subclasses, PR10.1 and PR10.2, but in silico predicted models of their three-dimensional structures revealed that they could be further divided based on size of the hydrophobic internal cavity and number of β-bulges. A comparison of the expression of two highly similar M. sativa subclass PR10.1 genes, MsPR10.1A and MsPR10.1B, predicted to have similar sized hydrophobic internal cavities, but a different number of β-bulges revealed differences in their expression patterns. MsPR10.1A was induced faster than MsPR10.1B by ABA, ethylene, and X. campestris pv. alfalfae, but slower than MsPR10.1B by harvesting and wounding. Unlike MsPR10.1A, MsPR10.1B expression was induced in non-harvested tissues following harvesting, but was not induced by heat treatment. Histochemical observations of Nicotiana benthamiana transformed with 657 bp of the MsPR10.1A promoter fused to the β-glucuronidase (GUS) gene showed that GUS expression was wound-inducible in leaves, which was consistent with MsPR10.1A expression in alfalfa leaves. GUS expression in stems and leaves was mostly in vascular tissue. The MsPR10.1A promoter may be valuable in controlling the expression in vascular tissues and disease resistance.

Transcriptome analysis of resistant and susceptible genotypes of Glycine tomentella during Phakopsora pachyrhizi infection reveals novel rust resistance genes

Soybean rust, caused by Phakopsora pachyrhizi, is a destructive foliar disease in nearly all soybean-producing countries. To identify genes controlling resistance to soybean rust, transcriptome profiling was conducted in resistant and susceptible Glycine tomentella genotypes triggered by P. pachyrhizi infection. Among 38,400 genes monitored using a soybean microarray, at 5% false discovery rate, 1,342 genes were identified exhibiting significant differential expression between uninfected and P. pachyrhizi-infected leaves at 12, 24, 48, and 72 h post-inoculation (hpi) in both rust-susceptible and rust-resistant genotypes. Differentially expressed genes were grouped into 12 functional categories, and among those, large numbers relate to basic plant metabolism. Transcripts for genes involved in the phenylpropanoid pathway were up-regulated early during rust infection. Similarly, genes coding for proteins related to stress and defense responses such as glutathione-S-transferases, peroxidases, heat shock proteins, and lipoxygenases were consistently up-regulated following infection at all four time points. Whereas, subsets of genes involved in cellular transport, cellular communication, cell cycle, and DNA processing were down-regulated. Quantitative real-time reverse-transcription polymerase chain reaction (qRT-PCR) on randomly selected genes from the different categories confirmed these findings. Of differentially expressed genes, those associated with the flavonoid biosynthesis pathway as well as those coding for peroxidases and lipoxygenases were likely to be involved in rust resistance in soybean, and would serve as good candidates for functional studies. These findings provided insights into mechanisms underlying resistance and general activation of plant defense pathways in response to rust infection.

Effects of a novel pathogenesis-related class 10 (PR-10) protein from Crotalaria pallida Roots with papain inhibitory activity against root-knot nematode Meloidogyne incognita

A novel pathogenesis-related class 10 (PR-10) protein with papain inhibitory activity, named CpPRI, was purified from Crotalaria pallida roots by ammonium sulfate precipitation followed by three reverse-phase high-performance liquid chromatographies (HPLCs). CpPRI is made up of a single polypeptide chain with a M(r) of 15 kDa, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). This protein exhibited a K(i) value of 1.8 x 10(-9) M and operates via a noncompetitive inhibition mechanism. The alignment of the N-terminal amino acid sequence of CpPRI with other proteins revealed its identity with PR-10 proteins. CpPRI acts against digestive proteinase from root-knot nematode Meloidogyne incognita and demonstrated nematostatic and nematicide effects on this parasite in bioassays. In a localization study, fluorescein-5-isothiocyanate (FITC)-CpPRI was observed to internalize and diffuse over the entire J2 body after 6 h of incubation. This fact could explain the natural tolerance of this plant species to nematodes.

Expression of pathogenesis-related protein PR-10 in sorghum floral tissues in response to inoculation with Fusarium thapsinum and Curvularia lunata

Differences in grain mould disease levels among different sorghum varieties grown in the same environment imply that host genes play a role in controlling disease severity. The fungi most often recovered from naturally infected sorghum grain, Fusarium thapsinum and Curvularia lunata, were used to inoculate a set of resistant and susceptible cultivars at anthesis in both field and glasshouse trials. In the field, 12 cultivars were inoculated with a mixture of F. thapsinum and C. lunata and, in the glasshouse, individual panicles from four selected cultivars were inoculated with spore suspensions of C. lunata, F. thapsinum, a mixture of the two or water to serve as a control. Based on grain mould severity ratings and germination tests on the seed from the field trial, Tx2911, Sureno, SC719-11E and SC650-11E displayed a high level of resistance to grain mould. To determine whether resistant and susceptible lines differed in response to the pathogens, PR-10 mRNA levels were measured using real-time reverse transcriptase-polymerase chain reaction. PR-10 is a protein with antifungal properties that has been associated with defence responses in sorghum and other plant species. In field tests, most, but not all, cultivars showed significant induction of normalized relative quantities of PR-10 after dual inoculation with spores of both C. lunata and F. thapsinum. Under glasshouse-controlled conditions, glumes of inoculated plants showed the clear induction of PR-10 mRNA, and the response was greater in resistant (Tx2911 and Sureno) than in susceptible (RTx430 and SC170-6-17) cultivars. Inoculation with spores from a single mould-inducing pathogen generally induced greater responses than when spores were combined. For RTx430, SC170-6-17 and Sureno, the response to C. lunata was greater, whereas Tx2911 showed a stronger response to F. thapsinum. The results indicate that the induction of PR-10 in sorghum glumes may be a factor useful in breeding programmes designed to combine multiple factors for resistance.

The RNA hydrolysis and the cytokinin binding activities of PR-10 proteins are differently performed by two isoforms of the Pru p 1 peach major allergen and are possibly functionally related

PR-10 proteins are a family of pathogenesis-related (PR) allergenic proteins playing multifunctional roles. The peach (Prunus persica) major allergen, Pru p 1.01, and its isoform, Pru p 1.06D, were found highly expressed in the fruit skin at the pit hardening stage, when fruits transiently lose their susceptibility to the fungal pathogen Monilinia spp. To investigate the possible role of the two Pru p 1 isoforms in plant defense, the recombinant proteins were expressed in Escherichia coli and purified. Light scattering experiments and circular dichroism spectroscopy showed that both proteins are monomers in solution with secondary structures typical of PR-10 proteins. Even though the proteins do not display direct antimicrobial activity, they both act as RNases, a function possibly related to defense. The RNase activity is different for the two proteins, and only that of Pru p 1.01 is affected in the presence of the cytokinin zeatin, suggesting a physiological correlation between Pru p 1.01 ligand binding and enzymatic activity. The binding of zeatin to Pru p 1.01 was evaluated using isothermal titration calorimetry, which provided information on the stoichiometry and on the thermodynamic parameters of the interaction. The structural architecture of Pru p 1.01 and Pru p 1.06D was obtained by homology modeling, and the differences in the binding pockets, possibly accounting for the observed difference in binding activity, were evaluated.

Biochemical and genetic characterization of Arabidopsis flavanone 3beta-hydroxylase

Flavanone 3beta-hydroxylase (F3H; EC 1.14.11.9) is a 2-oxoglutarate dependent dioxygenase that catalyzes the synthesis of dihydrokaempferol, the common precursor for three major classes of 3-hydroxy flavonoids, the flavonols, anthocyanins, and proanthocyanidins. This enzyme also competes for flux into the 3-deoxy flavonoid branch pathway in some species. F3H genes are increasingly being used, often together with genes encoding other enzymes, to engineer flavonoid synthesis in microbes and plants. Although putative F3H genes have been cloned in a large number of plant species, only a handful have been functionally characterized. Here we describe the biochemical properties of the Arabidopsis thaliana F3H (AtF3H) enzyme and confirm the activities of gene products from four other plant species previously identified as having high homology to F3H. We have also investigated the surprising "leaky" phenotype of AtF3H mutant alleles, uncovering evidence that two related flavonoid enzymes, flavonol synthase (EC 1.14.11.23) and anthocyanidin synthase (EC 1.14.11.19), can partially compensate for F3H in vivo. These experiments further indicate that the absence of F3H in these lines enables the synthesis of uncommon 3-deoxy flavonoids in the Arabidopsis seed coat.

The rice pathogen-related protein 10 (JIOsPR10) is induced by abiotic and biotic stresses and exhibits ribonuclease activity

We previously reported that rice blast fungus or jasmonic acid induced the expression of rice pathogenesis-related class 10 (JIOsPR10) proteins (Kim et al. 2003, 2004). However, no further studies have been carried out to examine the expression, localization, and enzymatic activity of this protein in either developmental tissues or in tissues under abiotic stress conditions. In this study, rice JIOsPR10 was examined by Western blot analysis, immunolocalization, and biochemical assays. Western blots revealed that the JIOsPR10 protein was expressed in developmental tissues, including in flower and root. The protein was also expressed under abiotic stresses, such as occurs during senescence and wounding. Using immunohistochemical techniques, we determined that expression of JIOsPR10 was localized to the palea of flower, in the exodermis, and inner part of the endodermis of the root. In senescencing tissues of leaf and coleoptiles, its expression was localized in vascular bundles. The RNase activity using JIOsPR10 recombinant protein was determined and abolished after treatment with DTT in a native in-gel assay. To test this, we created JIOsPR10 mutant proteins containing serine substitutions of amino acids C81S, C83S, or both and examined their RNase activities. The activity of the C83S mutant was decreased in the agarose gel assay compared to the wild type. Taken together, we hypothesize that the JIOsPR10 protein possesses RNase activity that is sensitive to DTT, suggesting the importance of the disulfide bonding between cysteine residues and that it might play a role in constitutive self-defense mechanisms in plants against biotic and abiotic stresses.

Biotechnology of flavonoids and other phenylpropanoid-derived natural products. Part I: Chemical diversity, impacts on plant biology and human health

Plant natural products derived from phenylalanine and the phenylpropanoid pathway are impressive in their chemical diversity and are the result of plant evolution, which has selected for the acquisition of large repertoires of pigments, structural and defensive compounds, all derived from a phenylpropanoid backbone via the plant-specific phenylpropanoid pathway. These compounds are important in plant growth, development and responses to environmental stresses and thus can have large impacts on agricultural productivity. While plant-based medicines containing phenylpropanoid-derived active components have long been used by humans, the benefits of specific flavonoids and other phenylpropanoid-derived compounds to human health and their potential for long-term health benefits have been only recognized more recently. In this part of the review, we discuss the diversity and biosynthetic origins of phenylpropanoids and particularly of the flavonoid and stilbenoid natural products. We then review data pertaining to the modes of action and biological properties of these compounds, referring on their effects on human health and physiology and their roles as plant defense and antimicrobial compounds. This review continues in Part II discussing the use of biotechnological tools targeting the rational reconstruction of multienzyme pathways in order to modify the production of such compounds in plants and model microbial systems for the benefit of agriculture and forestry.

Biochemical and molecular mechanisms involved in monogenic resistance responses to tomato powdery mildew

The monogenic genes Ol-1, ol-2, and Ol-4 confer resistance to tomato powdery mildew Oidium neolycopersici via different mechanisms. The biochemical mechanisms involved in these monogenic resistances were studied by monitoring through time the association of H2O2 and callose accumulation with hypersensitive response (HR) and papilla formation. Our results showed that H2O2 and callose accumulation are coupled with both Ol-1- and Ol-4-mediated HR-associated resistance as well as with the ol-2-mediated papillae-associated resistance. Further, the transcriptomal changes related to these monogenic resistances were studied by using cDNA-amplification fragment length polymorphism. The expression profiling clarified that 81% of DE-TDF (differentially expressed transcript-derived fragments) were up-regulated upon inoculation with O. neolycopersici in both the compatible and Ol-1-mediated incompatible interactions, though with a difference in expression timing. Of these DE-TDF, more than 70% were not detected in the Ol-4-mediated resistance, while 58% were expressed in the ol-2-mediated resistance, generally at later timepoints. Sequence information suggested that most of these DE-TDF are related to genes involved in either basal defense or establishment of compatibility. In addition, DE-TDF (19%) specifically expressed in different incompatible interactions were identified. Expression patterns of some DE-TDF and marker gene GluB suggested that papillae-associated resistance exploits a different defense pathway from that of HR-associated resistance.

A pathogenesis related protein, AhPR10 from peanut: an insight of its mode of antifungal activity

A pathogenesis related protein (AhPR10) is identified from a clone of 6-day old Arachis hypogaea L. (peanut) cDNA library. The clone expressed as a approximately 20 kDa protein in E. coli. Nucleotide sequence derived amino acid sequence of the coding region shows its homology with PR10 proteins having Betv1 domain and P loop motif. Recombinant AhPR10 has ribonuclease activity, and antifungal activity against the peanut pathogens Fusarium oxysporum and Rhizoctonia solani. Mutant protein AhPR10-K54N where lys54 is mutated to asn54 loses its ribonuclease and antifungal activities. FITC labeled AhPR10 and AhPR10-K54N are internalized by hyphae of F. oxysporum and R. solani but the later protein does not inhibit the fungal growth. This suggests that the ribonuclease function of AhPR10 is essential for its antifungal activity. Energy and temperature dependent internalization of AhPR10 into sensitive fungal hyphae indicate that internalization of the protein occurs through active uptake.

Role of defense/stress-related marker genes, proteins and secondary metabolites in defining rice self-defense mechanisms

Rice, a first cereal crop whose draft genome sequence from two subspecies (japonica-type cv. Nipponbare and indica-type 93-11) was available in 2002, along with its almost complete genome sequence in 2005, has drawn the attention of researchers worldwide because of its immense impact on human existence. One of the most critical research areas in rice is to discern the self-defense mechanism(s), an innate property of all living organisms. The last few decades have seen scattered research into rice responses to diverse environmental stimuli and stress factors. Our understanding on rice self-defense mechanism has increased considerably with accelerated research during recent years mainly due to identification and characterization of several defense/stress-related components, genes, proteins and secondary metabolites. As these identified components have been used to study the defense/stress pathways, their compilation in this review will undoubtedly help rice (and others) researchers to effectively use them as a potential marker for better understanding, and ultimately, in defining rice (and plant) self-defense response pathways.

A novel pathogenesis-related protein (SsPR10) from Solanum surattense with ribonucleolytic and antimicrobial activity is stress- and pathogen-inducible

A cDNA clone (designated as SsPR10, GenBank Accession Number AY660753 ) encoding a PR10 protein from yellow-fruit nightshade (Solanum surattense) was isolated and characterized. SsPR10 encoded a 160-amino-acid polypeptide with a predicted molecular mass of 17.58 kDa and pI of 5.29. Sequence alignments showed that SsPR10 had high identity (68.1%) with CaPR10, but had only about 31.7% identity with JIOsPR10 at the amino acid level. Genomic DNA gel blot analysis indicated that SsPR10 belonged to a multigene family. The constitutively expressed SsPR10 was detected to be the highest in roots of the sterile seedlings cultured in jars, while SsPR10 expression was the highest in old yellow leaves from the seedlings incubated with sap containing TMV. SsPR10 always expressed at slightly higher level in senescent leaves than in tender ones under both conditions. Further expression analysis revealed that the signaling components of defense/stress pathways (MeJA, SA, ABA, GA3, H2O2 and Cu2+) up-regulated significantly the SsPR10 mRNA levels over the control. However, darkness failed to induce SsPR10 expression and its expression was also inhibited by cold treatment. The SsPR10 was successfully expressed in Eschericha coli and the expressed protein was purified to near homogeneity. The dialytically renatured SsPR10 protein without phosphorylation exhibited ribonucleolytic activity against S. surattense leaf total RNA preparations and could inhibit hyphal growth of Pyricularia oryzae. Our findings suggest that the novel stress- and pathogen-inducible SsPR10 with ribonucleolytic and antimicrobial activity participates not only in the defense/stress response pathways but also in plants' growth, development and senescence.

Expression analysis of defence-related genes in grapevine leaves after inoculation with a host and a non-host pathogen

The expression of PR protein encoding genes and genes involved in the phenylpropanoid metabolism was analysed on grapevine leaves of susceptible and resistant cvs. in response to inoculation with the host-pathogen Plasmopara viticola and the non-host pathogen Pseudoperonospora cubensis, the downy mildew pathogen of cucumber. These experiments were conducted to elucidate whether or not grapevine plants susceptible to downy mildew exhibit an identical defence response after inoculation with the non-host pathogen. Expression analysis of defence-related genes revealed marked differences between the susceptible cultivar "Riesling" (Vitis vinifera) and the resistant cultivar "Gloire de Montpellier" (Vitis riparia). Whereas some genes seem to be expressed constitutively in "Gloire" or induced after an inoculation with both pathogens, expression of defence-related genes in Riesling was influenced mainly after inoculation with the non-host pathogen: PR-2, PR-3, PR-4, a PGIP gene, and especially genes encoding enzymes involved in anthocyanin biosynthesis (DFR, F3H, LDOX) were affected. Therefore, the occurrence of the respective products (flavans and other phenolics) in inoculated leaves was investigated with appropriate histological staining techniques. These stainings revealed a production of catechins and related phenolic compounds within the first 48 hai (hours after inoculation) with Ps. cubensis but not with P. viticola in Riesling, whereas in Gloire no further production was seen, which may be due to the high content of polyphenolics as observed in control leaves. In addition to the staining procedures, sporulation intensity was monitored on leaf discs. Pretreatments of leaf discs with Ps. cubensis led to a reduced browning reaction (as a result of a hypersensitive reaction) in Gloire and significantly reduced the intensity of sporulation in Riesling after a subsequent inoculation with P. viticola.

Birch PR-10c interacts with several biologically important ligands

PR-10c is a unique member of PR-10 proteins in birch, since it is the only one known to be post-translationally modified by glutathione and is not constitutively expressed in pollen. Both reduced and S-glutathiolated forms of PR-10c show low ribonuclease activity. However, the major function of the protein is apparently not yet resolved. Our protein-ligand interaction studies with saturation transfer difference (STD) NMR revealed that PR-10c interacts with several biologically important molecules, including cytokinin, flavonoid glycosides, sterols and emodin. Competition study with deoxycholate and kinetin revealed no statistically significant binding interference, indicating that these ligands have different binding sites in PR-10c. Ligand docking studies with a molecular model of PR-10c support the STD NMR results of ligand binding and binding epitopes, suggesting that there are three potential binding sites in PR-10c: two in the hydrophobic cavity and one in the glycine-rich loop. Our docking calculations suggested that only kinetin interacts with the glycine-rich loop, the binding occurring through its adenine moiety. Clear ligand specificity could be observed in the binding of nucleotide derivatives. S-glutathiolation of PR-10c did not affect kinetin binding. The present results suggest that birch PR-10c is a multifunctional protein, which has diverse roles in plant stress responses.

Proteomic profiling unravels insights into the molecular background underlying increased Aphanomyces euteiches-tolerance of Medicago truncatula

To investigate the molecular mechanisms underlying susceptibility of legumes to the root pathogen Aphanomyces euteiches (oomycota), comparative proteomic studies have been carried out. In a first approach, we have analysed two Medicago truncatula lines of the French CORE collection (F83.005-5 (R2002) and F83.005-9 (R2002)), which showed either increased or decreased susceptibility to A. euteiches as compared to the widely adopted line A17. Several proteins were identified to be differentially induced after pathogen challenge in the two M. truncatula accessions with altered disease susceptibility, whereof proteins with increased abundances in the more resistant line F83.005-9 could be involved in mechanisms that lead to an improved disease resistance. Among these proteins, we identified two proteasome alpha subunits, which might be involved in defense response. To broaden our studies on A. euteiches-tolerance of M. truncatula, we investigated two other phenomena that lead to an either increased A. euteiches-resistance or to an enhanced susceptibility. The topic of an enhanced plant resistance to A. euteiches was studied in plants showing a bioprotective effect of a pre-established arbuscular mycorrhiza (AM) symbiosis. Evaluation of root fresh weights and pathogen spreading in the root system clearly indicate that mycorrhizal plants show increased A. euteiches-resistance as compared to non-mycorrhizal plants. Proteome analyses revealed the induction of similar protein patterns as in the M. truncatula accessions with comparatively high resistance level to A. euteiches. In a third approach, increased A. euteiches susceptibility was effected by exogenous abscisic acid (ABA) application prior to root infection. Evaluation of the abundance levels of a group of pathogenesis related class 10 (PR10)-like proteins, which were previously identified to be regulated after A. euteiches infection, revealed a correlation between the abundance levels of these proteins and the A. euteiches infection level or severity.

Elicitation of defense related enzymes and resistance by L-methionine in pearl millet against downy mildew disease caused by Sclerospora graminicola

Induction of resistance to downy mildew in pearl millet was studied after treatment with L-methionine. The disease severity was drastically reduced in the seedlings after treatment with L-methionine. Northern hybridization was used to study the transcript (mRNA) accumulation of defense response genes upon treatment with L-methionine in pearl millet seedlings and the mechanism during the induction of resistance. The gene activation patterns in the highly resistant cultivar IP18294 were compared with those exhibited by the susceptible cultivar 7042S at various time intervals to determine if differences in timing or levels of transcript accumulation could be correlated with the differences in the susceptibility of pearl millet to the downy mildew pathogen, Sclerospora graminicola. The mRNA levels of genes for Pr-1a, beta-1,3-glucanase, chitinase, peroxidase, lipoxygenases and chalcone synthase showed an increase after inoculation with S. graminicola. Significant gene activation was observed in the susceptible cultivar 7042S after treatment with L-methionine followed by challenge inoculation with the downy mildew pathogen which was comparable to the resistant cultivar.

Identification of genes in cassava that are differentially expressed during infection with Xanthomonas axonopodis pv. manihotis

SUMMARY The cDNA-amplified fragment length polymorphism approach was used to identify differentially expressed transcripts from cassava infected by Xanthomonas axonopodis pv. manihotis (Xam). Approximately 3600 transcript-derived fragments (TDFs) were screened of which 340 were isolated. The nucleotide sequences of 250 TDFs were analysed and assembled into contigs and singletons. The amino acid sequences of their predicted products were compared with entries in databases and 63 of these clones showed homology to known plant genes. Of these, 32 showed similarity to plant defence proteins. Fifty-one TDFs corresponded to proteins of unknown function and 106 did not match any sequence in the public databases. Quantitative reverse transcription PCR was carried out with a selected set of gene transcripts that demonstrated an increase of expression during the infection. These results point out candidate genes that are associated with cassava resistance to Xam and reinforce the idea of a complex process occurring during this plant-pathogen interaction.

Proteomic analysis of pathogen-responsive proteins from rice leaves induced by rice blast fungus,Magnaporthe grisea

Proteomic approaches using two-dimensional gel electrophoresis (2-DE) were adopted to identify proteins from rice leaf that are differentially expressed in response to the rice blast fungus, Magnaporthe grisea. Microscopic observation of inoculated leaf with M. grisea revealed that callose deposition and hypersensitive response was clearly visible in incompatible interactions but excessive invading hypha with branches were evident in compatible interactions. Proteins were extracted from leaves 24, 48, and 72 hours after rice blast fungus inoculation. Eight proteins resolved on the 2-DE gels were induced or increased in the inoculated leaf. Matrix-assisted laser desorption/ionization-time of flight analysis of these differentially displayed proteins showed them to be two receptor-like protein kinases (RLK), two beta-1.3-glucanases (Glu1, Glu2), thaumatin-like protein (TLP), peroxidase (POX 22.3), probenazole-inducible protein (PBZ1), and rice pathogenesis-related 10 (OsPR-10). Of these proteins, RLK, TLP, PBZ, and OsPR-10 proteins were induced more in the incompatible interactions than in compatible ones. A phytohormone, jasmonic acid also induced all eight proteins in leaves. To confirm whether the expression profile is equal to the 2-DE data, seven cDNA clones were used as probes in Northern hybridization experiments using total RNA from leaf tissues inoculated with incompatible and compatible rice blast fungal races. The genes encoding POX22.3, Glu1, Glu2, TLP, OsRLK, PBZ1, and OsPR-10 were activated in inoculated leaves, with TLP, OsRLK, PBZ1, and OsPR-10 being expressed earlier and more in incompatible than in compatible interactions. These results suggest that early and high induction of these genes may provide host plants with leading edges to defend themselves. The localization of two rice PR-10 proteins, PBZ1 and OsPR-10, was further examined by immunohistochemical analysis. PBZ1 accumulated highly in mesophyll cells under the attachment site of the appressorium. In contrast, OsPR-10 expression was mainly localized to vascular tissue.

A novel rice PR10 protein, RSOsPR10, specifically induced in roots by biotic and abiotic stresses, possibly via the jasmonic acid signaling pathway

Plant roots have important roles not only in absorption of water and nutrients, but also in stress tolerance such as desiccation, salt, and low temperature. We have investigated stress-response proteins from rice roots using 2-dimensional polyacrylamide-gel electrophoresis and found a rice protein, RO-292, which was induced specifically in roots when 2-week-old rice seedlings were subjected to salt and drought stress. The full-length RO-292 cDNA was cloned, and was determined to encode a protein of 160 amino acid residues (16.9 kDa, pI 4.74). The deduced amino acid sequence showed high similarity to known rice PR10 proteins, OsPR10a/PBZ1 and OsPR10b. RO-292 mRNA accumulated rapidly upon drought, NaCl, jasmonic acid and probenazole, but not by exposure to low temperature or by abscisic acid and salicylic acid. The RO-292 gene was also up-regulated by infection with rice blast fungus. Interestingly, induction was observed almost exclusively in roots, thus we named the gene RSOsPR10 (root specific rice PR10). The present results indicate that RSOsPR10 is a novel rice PR10 protein, which is rapidly induced in roots by salt, drought stresses and blast fungus infection possibly through activation of the jasmonic acid signaling pathway, but not the abscisic acid and salicylic acid signaling pathway.

Pathogenesis-related protein 10 isolated from hot pepper functions as a ribonuclease in an antiviral pathway

A hot pepper (Capsicum annuum) cDNA clone encoding pathogenesis-related protein 10 (CaPR-10) was isolated by differential screening of a cDNA library prepared from pepper leaves inoculated with tobacco mosaic virus pathotype (TMV-P0). CaPR-10 transcripts were induced in the incompatible interaction with TMV-P0 or Xanthomonas campestris pv. vesicatoria (Xcv) but not induced in the compatible interaction. Characterization of enzymatic properties of CaPR-10 indicated that the recombinant protein exhibits a ribonucleolytic activity against TMV RNA, as well as against pepper total RNA, and shows its putative antiviral activity in several conditions. The CaPR-10 protein existed at very low level in leaf tissue but was dramatically induced as soon as plants were inoculated with TMV-P0, and this was correlated with the increase of its ribonucleolytic activity. Immunoblot analysis and pull-down assays using proteins extracted from pepper leaves showed that TMV-P0 inoculation led to the phosphorylation of CaPR-10, a modification that should affect its capacity for RNase function. We present data that the induction and subsequent phosphorylation of CaPR-10 increased its ribonucleolytic activity to cleave invading viral RNAs, and this activity should be important to its antiviral pathway during viral attack in vivo.

Differential defense reactions in leaf tissues of barley in response to infection by Rhynchosporium secalis and to treatment with a fungal avirulence gene product

Expression of defense-associated genes was analyzed in leaf tissues of near-isogenic resistant and susceptible barley cultivars upon infection by Rhynchosporium secalis. The genes encoding pathogenesis-related (PR) proteins PR-1, PR-5, and PR-9 are specifically expressed in the mesophyll of resistant plants, whereas a germin-like protein (OxOLP) is synthesized in the epidermis irrespective of the resistance genotype. Restriction-mediated differential display was employed to identify additional epidermis-specific genes. This resulted in the detection of another PR gene, PR-10, along with a lipoxygenase gene, LoxA, and a gene of unknown function, pI2-4, which are specifically induced in the epidermis of resistant plants. The gene encoding a putative protease inhibitor, SD10, is preferentially but not exclusively expressed in the epidermis. The fungal avirulence gene product NIP1 triggers the induction of the four PR genes only. At least two additional elicitors, therefore, must be postulated, one for the unspecific induction of OxOLP and one for the resistance-specific induction of LoxA, pI2-4, and SD10. PR-10 expression can be assumed to be the consequence of NIP1 perception by epidermis cells. In contrast, gene expression in the mesophyll is likely to be triggered by an as yet unknown signal that appears to originate in the epidermis and that is strongly amplified in the mesophyll.

Molecular cloning and characterization of a novel Jasmonate inducible pathogenesis-related class 10 protein gene, JIOsPR10, from rice (Oryza sativa L.) seedling leaves

A novel rice (Oryza sativa L.) gene, homologous to a sorghum pathogenesis-related class 10 protein gene, was cloned from a cDNA library prepared from 2-week-old jasmonic acid-treated rice seedling leaves, and named as JIOsPR10 (jasmonate inducible). JIOsPR10 encoded a 160-amino-acid polypeptide with a predicted molecular mass of 17,173.23 Da and a pI of 5.84. JIOsPR10 was highly similar (77%) to the sorghum PR10 protein, but showed less than 55% similarity with other identified PR10s at the amino acid level. Genomic Southern analyses indicated the presence of related genes in the rice genome. The JIOsPR10 transcript was not detected in the healthy leaves, and was not induced after cut. Further expression analysis revealed that the signaling components of defense/stress pathways, jasmonate, salicylate, and H(2)O(2) significantly up-regulated the JIOsPR10 mRNA over the cut control, whereas two other stress regulators, ethylene and abscisic acid, failed to induce its expression. Interestingly the protein phosphatase (PP) inhibitors, cantharidin, endothall, and okadaic acid, rapidly and potently up-regulated the JIOsPR10 expression, suggesting involvement of the phosphorylation/dephosphorylation events. Additionally, the inducible expression of the JIOsPR10 gene was influenced by light signal(s). Finally, the blast pathogen (Magnaporthe grisea) also specifically elicited the accumulation of JIOsPR10 mRNA in leaves. Induction of the JIOsPR10 gene expression by signaling molecules, PP inhibitors and pathogen attack, strongly indicate a role for this novel gene in rice self-defense/stress response(s).

Characterization of a PR-10 pathogenesis-related gene family induced in rice during infection with Magnaporthe grisea

A partial cDNA with homology to the PR-10 class of pathogenesis-related proteins was used to screen a rice genomic library. One 16-kb genomic clone contained three genes with PR-10 similarity. These genes, RPR10a, RPR10b, and RPR10c, were arranged in tandem and separated by approximately 2.5 kb. RPR10a cDNA was obtained by reverse transcription-polymerase chain reaction, and sequence analysis revealed that RPR10a and RPR10b encode predicted proteins of 158 and 160 amino acids, respectively, and share 71% amino acid identity. RPR10c appears to be a nonfunctional pseudogene. Gene-specific probes were used to study transcript accumulations of the three RPR10 genes in rice plants following inoculation with Magnaporthe grisea. RPR10a transcripts were induced from a low basal level within 12 h after inoculation and showed a second higher level induction at 48 h, which continued throughout the 144 h it was examined. In addition, RPR10a was induced strongly by salicylic and jasmonic acid applications to rice plants. Transcripts of RPR10b also were enhanced by M. grisea, but were not strongly visible until 48 h after inoculation. Tissue prints of M. grisea-infected rice leaves when the RPR10a-specific probe was used indicate that RPR10a is expressed most strongly in a localized fashion in response to the pathogen.

Nonhost resistance and nonspecific plant defenses

In the past year, most of the advances in our understanding of nonhost resistance to plant pathogens have been incremental. Highlights include the discovery of a general bacterial elicitor of plant defenses, the description of more similarities between the hypersensitive response and animal programmed cell death, and a growing appreciation of the cell wall as the site of initiation and expression of nonhost resistance towards fungi.