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

Impact of Heat Stress on Expression of Wheat Genes Responsive to Hessian Fly Infestation

Heat stress compromises wheat (Triticum aestivium) resistance to Hessian fly (HF, Mayetiola destructor (Say)). This study aimed to investigate the impact of heat stress on transcript expression of wheat genes associated with resistance to HF infestation under normal and heat-stressed conditions. To this end, ‘Molly’, a wheat cultivar containing the resistance gene H13, was subjected to HF infestation, heat stress, and the combination of HF infestation and heat stress. Our RNA-Seq approach identified 21 wheat genes regulated by HF infestation under normal temperatures (18 °C) and 155 genes regulated by HF infestation when plants were exposed to 35 °C for 6 h. Three differentially expressed genes (DEGs) from the RNA-Seq analysis were selected to validate the gene function of these DEGs using the RT-qPCR approach, indicating that these DEGs may differentially contribute to the expression of wheat resistance during the early stage of wheat–HF interaction under various stresses. Moreover, the jasmonate ZIM domain (JAZ) gene was also significantly upregulated under these treatments. Our results suggest that the genes in heat-stressed wheat plants are more responsive to HF infestation than those in plants growing under normal temperature conditions, and these genes in HF-infested wheat plants are more responsive to heat stress than those in plants without infestation.

Review: Biological functions of major latex-like proteins in plants

Major latex-like proteins (MLPs) have been identified in dicots and monocots. They are members of the birch pollen allergen Bet v 1 family as well as pathogenesis-related proteins class 10. MLPs have two main features. One is binding affinity toward various hydrophobic compounds, such as long-chain fatty acids, steroids, and systemic acquired resistance signals, via its internal hydrophobic cavity or hydrophobic residues on its surface. MLPs transport such compounds to other organs via phloem and xylem vessels and contribute to the expression of physiologically important ligands' activity in the particular organs. The second feature is responses to abiotic and biotic stresses. MLPs are involved in drought and salt tolerance through the mediation of plant hormone signaling pathways. MLPs generate resistance against pathogens by the induction of pathogenesis-related protein genes. Therefore, MLPs play crucial roles in drought and salt tolerance and resistance against pathogens. However, knowledge of MLPs is fragmented, and an overview of them is needed. Herein, we summarize the current knowledge of the biological functions of MLPs, which to our knowledge, is the first review about MLPs that has been reported.

Biotechnological Perspectives of Omics and Genetic Engineering Methods in Alfalfa

For several decades, researchers are working to develop improved major crops with better adaptability and tolerance to environmental stresses. Forage legumes have been widely spread in the world due to their great ecological and economic values. Abiotic and biotic stresses are main factors limiting legume production, however, alfalfa (Medicago sativa L.) shows relatively high level of tolerance to drought and salt stress. Efforts focused on alfalfa improvements have led to the release of cultivars with new traits of agronomic importance such as high yield, better stress tolerance or forage quality. Alfalfa has very high nutritional value due to its efficient symbiotic association with nitrogen-fixing bacteria, while deep root system can help to prevent soil water loss in dry lands. The use of modern biotechnology tools is challenging in alfalfa since full genome, unlike to its close relative barrel medic (Medicago truncatula Gaertn.), was not released yet. Identification, isolation, and improvement of genes involved in abiotic or biotic stress response significantly contributed to the progress of our understanding how crop plants cope with these environmental challenges. In this review, we provide an overview of the progress that has been made in high-throughput sequencing, characterization of genes for abiotic or biotic stress tolerance, gene editing, as well as proteomic and metabolomics techniques bearing biotechnological potential for alfalfa improvement.

Comparative transcriptome analysis of the interaction between Actinidia chinensis var. chinensis and Pseudomonas syringae pv. actinidiae in absence and presence of acibenzolar-S-methyl

BACKGROUND

Since 2007, bacterial canker caused by Pseudomonas syringae pv. actinidiae (Psa) has become a pandemic disease leading to important economic losses in every country where kiwifruit is widely cultivated. Options for controlling this disease are very limited and rely primarily on the use of bactericidal compounds, such as copper, and resistance inducers. Among the latter, the most widely studied is acibenzolar-S-methyl. To elucidate the early molecular reaction of kiwifruit plants (Actinidia chinensis var. chinensis) to Psa infection and acibenzolar-S-methyl treatment, a RNA seq analysis was performed at different phases of the infection process, from the epiphytic phase to the endophytic invasion on acibenzolar-S-methyl treated and on non-treated plants. The infection process was monitored in vivo by confocal laser scanning microscopy.

RESULTS

De novo assembly of kiwifruit transcriptome revealed a total of 39,607 transcripts, of which 3360 were differentially expressed during the infection process, primarily 3 h post inoculation. The study revealed the coordinated changes of important gene functional categories such as signaling, hormonal balance and transcriptional regulation. Among the transcription factor families, AP2/ERF, MYB, Myc, bHLH, GATA, NAC, WRKY and GRAS were found differentially expressed in response to Psa infection and acibenzolar-S-methyl treatment. Finally, in plants treated with acibenzolar-S-methyl, a number of gene functions related to plant resistance, such as PR proteins, were modulated, suggesting the set-up of a more effective defense response against the pathogen. Weighted-gene coexpression network analysis confirmed these results.

CONCLUSIONS

Our work provides an in-depth description of the plant molecular reactions to Psa, it highlights the metabolic pathway related to acibenzolar-S-methyl-induced resistance and it contributes to the development of effective control strategies in open field.

Molecular Cloning and Expression Analysis of hyp-1 Type PR-10 Family Genes in Hypericum perforatum

Hypericum perforatum L. is an important medicinal plant for the treatment of depression. The plant contains bioactive hypericins that accumulate in dark glands present especially in reproductive parts of the plant. In this study, pathogenesis-related class 10 (PR-10) family genes were identified in H. perforatum, including three previously unidentified members with sequence homology to hyp-1, a phenolic coupling protein that has earlier been suggested to participate in biosynthesis and binding/transportation of hypericin. The PR-10 genes showed constitutive but variable expression patterns in different H. perforatum tissues. They were all expressed at relatively high levels in leaves, variably in roots and low levels in stem and reproductive parts of the plant with no specific association with dark glands. The gene expression was up-regulated in leaves after salicylic acid, abscisic acid and wounding treatments but with variable levels. To study exact location of the gene expression, in situ hybridization of hyp-1 transcripts was performed and the accumulation of the Hyp-1 protein was examined in various tissues. The presence of Hyp-1 protein in H. perforatum tissues mostly paralleled with the mRNA levels. In situ RNA hybridization localized the hyp-1 transcripts predominantly in vascular tissues in root and stem, while in leaf the mRNA levels were high also in mesophyll cells in addition to vasculature. Our results indicate that the studied PR-10 genes are likely to contribute to the defense responses in H. perforatum. Furthermore, despite the location of the hyp-1 transcripts in vasculature, no support for the transportation of the Hyp-1 protein to dark glands was found in the current study. The present results together with earlier data question the role of the hyp-1 as a key gene responsible for the hypericin biosynthesis in dark glands of H. perforatum.

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.

A Novel Pathogenesis-Related Class 10 Protein Gly m 4l, Increases Resistance upon Phytophthora sojae Infection in Soybean (Glycine max [L.] Merr.)

Phytophthora root and stem rot of soybean, caused by Phytophthora sojae (P. sojae), is a destructive disease in many soybean planting regions worldwide. In a previous study, an expressed sequence tag (EST) homolog of the major allergen Pru ar 1 in apricot (Prunus armeniaca) was identified up-regulated in the highly resistant soybean 'Suinong 10' infected with P. sojae. Here, the full length of the EST was isolated using rapid amplification of cDNA ends (RACE). It showed the highest homology of 53.46% with Gly m 4 after comparison with the eight soybean allergen families reported and was named Gly m 4-like (Gly m 4l, GenBank accession no. HQ913577.1). The cDNA full length of Gly m 4l was 707 bp containing a 474 bp open reading frame encoding a polypeptide of 157 amino acids. Sequence analysis suggests that Gly m 4l contains a conserved 'P-loop' (phosphate-binding loop) motif at residues 47-55 aa and a Bet v 1 domain at residues 87-120 aa. The transcript abundance of Gly m 4l was significantly induced by P. sojae, salicylic acid (SA), NaCl, and also responded to methyl jasmonic acid (MeJA) and ethylene (ET). The recombinant Gly m 4l protein showed RNase activity and displayed directly antimicrobial activity that inhibited hyphal growth and reduced zoospore release in P. sojae. Further analyses showed that the RNase activity of the recombinant protein to degrading tRNA was significantly affected in the presence of zeatin. Over-expression of Gly m 4l in susceptible 'Dongnong 50' soybean showed enhanced resistance to P. sojae. These results indicated that Gly m 4l protein played an important role in the defense of soybean against P. sojae infection.

Isolation and characterization of a pathogenesis-related protein 10 gene (GmPR10) with induced expression in soybean (Glycine max) during infection with Phytophthora sojae

In previous study, a cDNA library enriched for mRNAs encoding ESTs that increased in abundance during infection with Phytophthora sojae was constructed by suppression subtractive hybridization from leaf tissues of a high resistant soybean, and an EST homologous to the class 10 of pathogenesis-related (PR) proteins was identified to be up-regulated by microarray and real-time PCR. Here, the full-length cDNA (termed GmPR10, GenBank accession number FJ960440; ADC31789.1) of the EST was isolated by rapid amplification of cDNA ends, and contains an open reading frame of 474 bp. The GmPR10 protein included a "P-loop'' motif. The constitutive transcript abundance of GmPR10 in soybean was the highest in leaves, followed by roots and stems. Further analysis showed that GmPR10 mRNA abundance was increased during infection with P. sojae following leaf treatments with gibberellin (GA3), hydrogen peroxide (H2O2), salicylic acid (SA), and abscisic acid (ABA). The dialytically renatured GmPR10 protein significantly inhibited P. sojae hyphal growth and exhibited RNase activity. Transgenic tobacco and soybean plants overexpressing GmPR10 showed increased resistance to P. nicotianae Breda and P. sojae, respectively. These results suggest that the GmPR10 protein plays an important role in host defense against P. sojae infection. To the best of our knowledge, this is the first report on the functional characterization of a PR10 protein from soybean in defense against P. sojae.

Pathogenesis related-10 proteins are small, structurally similar but with diverse role in stress signaling

Pathogenesis related-10 proteins are small proteins with cytosolic localization, conserved three dimensional structures and single intron at 185 bp position. These proteins have a broad spectrum of roles significantly in biotic and abiotic stresses. The RNase activity, ligand binding activity, posttranslational modification (phosphorylation) and phytohormone signaling provide some information into the mechanism of the regulation of PR-10 proteins, however the presence of isoforms makes it difficult to decipher its exact mode of function. The involvement of phosphorylation/dephosphorylation events in its activation is interesting and provides unique and unbiased insights into the complexity of its regulation. Studies on upstream region of different PR-10 genes indicate the presence of cis-acting elements for WRKY, RAVI, bZ1P, ERF, SEBF and Pti4 transcription factors indicating their role in regulating PR-10 promoter. In this review, we discuss in detail the structure and mechanism of regulation of PR-10 proteins.

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.

Evaluation of the allergenicity potential of TcPR-10 protein from Theobroma cacao

BACKGROUND

The pathogenesis related protein PR10 (TcPR-10), obtained from the Theobroma cacao-Moniliophthora perniciosa interaction library, presents antifungal activity against M. perniciosa and acts in vitro as a ribonuclease. However, despite its biotechnological potential, the TcPR-10 has the P-loop motif similar to those of some allergenic proteins such as Bet v 1 (Betula verrucosa) and Pru av 1 (Prunus avium). The insertion of mutations in this motif can produce proteins with reduced allergenic power. The objective of the present work was to evaluate the allergenic potential of the wild type and mutant recombinant TcPR-10 using bioinformatics tools and immunological assays.

METHODOLOGY/PRINCIPAL FINDINGS

Mutant substitutions (T10P, I30V, H45S) were inserted in the TcPR-10 gene by site-directed mutagenesis, cloned into pET28a and expressed in Escherichia coli BL21(DE3) cells. Changes in molecular surface caused by the mutant substitutions was evaluated by comparative protein modeling using the three-dimensional structure of the major cherry allergen, Pru av 1 as a template. The immunological assays were carried out in 8-12 week old female BALB/c mice. The mice were sensitized with the proteins (wild type and mutants) via subcutaneous and challenged intranasal for induction of allergic airway inflammation.

CONCLUSIONS/SIGNIFICANCE

We showed that the wild TcPR-10 protein has allergenic potential, whereas the insertion of mutations produced proteins with reduced capacity of IgE production and cellular infiltration in the lungs. On the other hand, in vitro assays show that the TcPR-10 mutants still present antifungal and ribonuclease activity against M. perniciosa RNA. In conclusion, the mutant proteins present less allergenic potential than the wild TcPR-10, without the loss of interesting biotechnological properties.

Impact of pr-10a overexpression on the cryopreservation success of Solanum tuberosum suspension cultures

Although many genes are supposed to be a part of plant cell tolerance mechanisms against osmotic or salt stress, their influence on tolerance towards stress during cryopreservation procedures has rarely been investigated. For instance, the overexpression of the pathogenesis-related gene 10a (pr-10a) leads to improved osmotic tolerance in a transgenic cell culture of Solanum tuberosum cv. Désirée. In this study, a cryopreservation method, consisting of osmotic pretreatment, cryoprotection with DMSO and controlled-rate freezing, was used to characterize the relation between cryopreservation success and pr-10a expression in suspension cultures of S. tuberosum wild-type cells and cells overexpressing pathogenesis-related protein 10a (Pr-10a). By varying the sorbitol concentration, thus modifying the strength of the osmotic stress during the pretreatment phase, it can be shown that the wild type can successfully be cryopreserved only in a relatively narrow range of sorbitol concentrations, while the pr-10a overexpression leads to an enhanced cryopreservation success over the whole range of applied sorbitol concentrations. Together with transcription data we show that the pr-10a overexpression causes an enhanced osmotic tolerance, which in turn leads to enhanced cryopreservability, but also indicates a role of pr-10a in signal transduction. An increased cryopreservability of the transgenic cell line occurs for pretreatments longer than 24 h. Since both genotypes, characterized by distinct baseline levels of expression, exhibited similar patterns of expression induction, the induction of pr-10a appears to be a key step in the stress signal transduction of plant cells under osmotic stress.