Organization of phenylalanine ammonia lyase (PAL), acidic PR-5 and osmotin-like (OSM) defence-response gene families in the potato genome

Cloning and characterization of KoOsmotin from mangrove plant Kandelia obovata under cold stress

BACKGROUND

Low temperature is a major abiotic stress that seriously limits mangrove productivity and distribution. Kandelia obovata is the most cold-resistance specie in mangrove plants, but little is known about the molecular mechanism underlying its resistance to cold. Osmotin is a key protein associated with abiotic and biotic stress response in plants but no information about this gene in K. obovata was reported.

RESULTS

In this study, a cDNA sequence encoding osmotin, KoOsmotin (GenBank accession no. KP267758), was cloned from mangrove plant K. obovata. The KoOsmotin protein was composed of 221 amino acids and showed a calculated molecular mass of 24.11 kDa with pI 4.92. The KoOsmotin contained sixteen cysteine residues and an N-terminal signal peptide, which were common signatures to most osmotins and pathogenesis-related 5 proteins. The three-dimensional (3D) model of KoOsmotin, contained one α-helix and eleven β-strands, was formed by three characteristic domains. Database comparisons of the KoOsmotin showed the closest identity (55.75%) with the osmotin 34 from Theobroma cacao. The phylogenetic tree also revealed that the KoOsmotin was clustered in the branch of osmotin/OLP (osmotin-like protien). The KoOsmotin protein was proved to be localized to both the plasma membrane and cytoplasm by the subcellular localization analysis. Gene expression showed that the KoOsmotin was induced primarily and highly in the leaves of K. obovata, but less abundantly in stems and roots. The overexpressing of KoOsmotin conferred cold tolerance in Escherichia coli cells.

CONCLUSION

As we known, this is the first study to explore the osmotin of K. obovata. Our study provided valuable clues for further exploring the function of KoOsmotin response to stress.

Common Mycorrhizal Network Induced JA/ET Genes Expression in Healthy Potato Plants Connected to Potato Plants Infected by Phytophthora infestans

Most plants are connected belowground via common mycorrhizal networks (CMNs). In their presence, the transmission of warning signals from diseased to uninfected plants has been reported. However, current studies have all been conducted in pots making it difficult to discriminate direct from indirect contribution of hyphae to the transmission of the signals. Here, we conducted an in vitro study with potato plantlets connected by a CMN of the arbuscular mycorrhizal fungus Rhizophagus irregularis. The plantlets were grown in physically separated compartments and their connection ensured only by the CMN. The donor potato plantlets were infected by Phytophthora infestans and defense genes analyzed 24, 48 and 120 h post-infection (hpi) in the uninfected receiver potato plantlets. Twenty-four hpi by the pathogen, PAL, PR-1b, ERF3, and LOX genes were significantly upregulated, whereas no significant transcript variation was noticed 48 and 120 hpi. The exact nature of the warning signals remains unknown but was not associated to microorganisms other than the AMF or to diffusion mechanisms through the growth medium or induced by volatile compounds. The defense response appeared to be transitory and associated with the jasmonic acid or ethylene pathway. These findings demonstrate the direct involvement of hyphae in the transmission of warning signals from diseased to uninfected potato plantlets and their indubitable role in providing a route for activating defense responses in uninfected plants.

Application of Glycerol for Induced Powdery Mildew Resistance in Triticum aestivum L

Previous work has demonstrated that glycerol-3-phosphate (G3P) and oleic acid (18:1) are two important signal molecules associated with plant resistance to fungi. In this article, we provide evidence that a 3% glycerol spray application 1-2 days before powdery mildew infection and subsequent applications once every 4 days was sufficient to stimulate the plant defense responses without causing any significant damage to wheat leaves. We found that G3P and oleic acid levels were markedly induced by powdery mildew infection. In addition, TaGLI1 (encoding a glycerol kinase) and TaSSI2 (encoding a stearoylacyl carrier protein fatty acid desaturase), two genes associated with the glycerol and fatty acid (FA) pathways, respectively, were induced by powdery mildew infection, and their promoter regions contain some fungal response elements. Moreover, exogenous application of glycerol increased the G3P level and decreased the level of oleic acid (18:1). Glycerol application induced the expression of pathogenesis-related (PR) genes (TaPR-1, TaPR-2, TaPR-3, TaPR-4, and TaPR-5), induced the generation of reactive oxygen species (ROS) before powdery mildew infection, and induced salicylic acid (SA) accumulation in wheat leaves. Further, we sprayed glycerol in a wheat field and found that it significantly (p < 0.05) reduced the severity of powdery mildew disease and lessened disease-associated kernel weight loss, all without causing any noticeable degradation in wheat seed quality.

IbACP, a sixteen-amino-acid peptide isolated from Ipomoea batatas leaves, induces carcinoma cell apoptosis

A 16-amino-acid peptide was isolated from the leaves of sweet potato. The peptide caused a rapid alkalinization response in tomato suspension culture media, a characteristic of defense peptides in plants. No post-translational modification was observed on the peptide according to MALDI-MS analysis. We have named the peptide Ipomoea batatas anti-cancer peptide (IbACP). IbACP also was shown with the ability to dose-dependently inhibit Panc-1, a pancreatic cancer line, cell proliferation. The morphological observations of the Panc-1 cells by phase contrast microscopy showed significant changes after treatment with IbACP. Moreover, caspase-3 and PARP [poly(ADP-ribose) polymerase] were activated by IbACP treatment, followed by cell death. An increase in the levels of cleaved caspase-3 and -9 was also detected by an immunoblot assay after treatment with IbACP. In addition, genomic DNA fragmentation and decreased cellular proliferation were induced when IbACP was supplied to the Panc-1 cells, further demonstrating its biological relevance. The combined data indicates that IbACP peptide may have an important role in the regulation of cellular proliferation by inducing and promoting apoptosis through the mitochondrial apoptotic pathway. This report also showed that IbACP peptide contains potent anti-cancer effects and may play an important role in herbal medicine development.

Conservation, Divergence, and Genome-Wide Distribution of PAL and POX A Gene Families in Plants

Genome-wide identification and phylogenetic and syntenic comparison were performed for the genes responsible for phenylalanine ammonia lyase (PAL) and peroxidase A (POX A) enzymes in nine plant species representing very diverse groups like legumes (Glycine max and Medicago truncatula), fruits (Vitis vinifera), cereals (Sorghum bicolor, Zea mays, and Oryza sativa), trees (Populus trichocarpa), and model dicot (Arabidopsis thaliana) and monocot (Brachypodium distachyon) species. A total of 87 and 1045 genes in PAL and POX A gene families, respectively, have been identified in these species. The phylogenetic and syntenic comparison along with motif distributions shows a high degree of conservation of PAL genes, suggesting that these genes may predate monocot/eudicot divergence. The POX A family genes, present in clusters at the subtelomeric regions of chromosomes, might be evolving and expanding with higher rate than the PAL gene family. Our analysis showed that during the expansion of POX A gene family, many groups and subgroups have evolved, resulting in a high level of functional divergence among monocots and dicots. These results will act as a first step toward the understanding of monocot/eudicot evolution and functional characterization of these gene families in the future.

SpUSP, an annexin-interacting universal stress protein, enhances drought tolerance in tomato

Universal stress protein (USP) appears to play an active role in the abiotic stress response, but their functions remain largely unknown in plants. A USP gene (SpUSP) was cloned from wild tomato (Solanum pennellii) and functionally characterized in cultivated tomato in the present study. The SpUSP transcript is abundantly accumulated in leaf stomata and its expression varied with the circadian rhythm. SpUSP was remarkably induced by dehydration, salt stress, oxidative stress, and the phytohormone abscisic acid (ABA) etc. This protein was predominantly localized in the nucleus and cell membrane. Overexpressing SpUSP increased drought tolerance of tomato in the seedling and adult stages. Under drought stress, the ABA content significantly increased in the SpUSP-overexpressing plants, which induced stomatal closure and reduced water loss, leading to the enhancement of drought tolerance. Based on the microarray data, a large number of chlorophyll a/b-binding proteins and photosystem-related genes were up-regulated in the SpUSP-overexpressing plants under drought conditions, which possibly enhanced the stomatal sensivitity to ABA and maintained the photosynthetic function. SpUSP overexpression also alleviated the oxidative damage accompanied by oxidative stress-responsive gene activation and osmolyte accumulation. Annexin (SGN-U314161) was found to interacte with SpUSP in the yeast two-hybrid method. This interaction was further confirmed by the bimolecular fluorescence complementation assay. The present study demonstrated that the annexin-interacting SpUSP plays important roles in the drought tolerance of tomato by influencing ABA-induced stomatal movement, increasing photosynthesis, and alleviating oxidative stress.

Arbuscular mycorrhisation with Glomus irregulare induces expression of potato PR homologues genes in response to infection by Fusarium sambucinum

Arbuscular mycorrhizal fungi (AMF) are symbiotic, root-inhabiting fungi colonising a wide range of vascular plant species. We previously showed that AMF modulate the expression of mycotoxin genes in Fusarium sambucinum. Here, we tested the hypothesis that AMF may induce defence responses in potato to protect against infection with F. sambucinum. We analysed the response of AMF-colonised potato plants to the pathogenic fungus F. sambucinum by monitoring the expression of defence-related genes ChtA3, gluB, CEVI16, OSM-8e and PR-1. In response to F. sambucinum infection, we found that the AMF treatment upregulated the expression of all defence genes except OSM-8e in potato roots at 72 and 120h post infection (hpi). However, we found variable transcriptional regulation with gluB and CEVI16 in shoots at both times 72 and 120hpi in AMF-colonisation and infected plants. Overall, differential regulation of defence-related genes in leaf tissues indicate that AMF are a systemic bio-inducer and their effect could extend into non-infected parts. Thus, AMF significantly suppressed disease severity of F. sambucinum on potato plants compared with those infected and non-mycorrhizal plants. Furthermore, the AMF treatment decreased the negative effects of F. sambucinum on biomass and potato tuber production.

The Ve-mediated resistance response of the tomato to Verticillium dahliae involves H2O2, peroxidase and lignins and drives PAL gene expression

BACKGROUND

Verticillium dahliae is a fungal pathogen that infects a wide range of hosts. The only known genes for resistance to Verticillium in the Solanaceae are found in the tomato (Solanum lycopersicum) Ve locus, formed by two linked genes, Ve1 and Ve2. To characterize the resistance response mediated by the tomato Ve gene, we inoculated two nearly isogenic tomato lines, LA3030 (ve/ve) and LA3038 (Ve/Ve), with V. dahliae.

RESULTS

We found induction of H2O2 production in roots of inoculated plants, followed by an increase in peroxidase activity only in roots of inoculated resistant plants. Phenylalanine-ammonia lyase (PAL) activity was also increased in resistant roots 2 hours after inoculation, while induction of PAL activity in susceptible roots was not seen until 48 hours after inoculation. Phenylpropanoid metabolism was also affected, with increases in ferulic acid, p-coumaric acid, vanillin and p-hydroxybenzaldehyde contents in resistant roots after inoculation. Six tomato PAL cDNA sequences (PAL1 - PAL6) were found in the SolGenes tomato EST database. RT-PCR analysis showed that these genes were expressed in all organs of the plant, albeit at different levels. Real-time RT-PCR indicated distinct patterns of expression of the different PAL genes in V. dahliae-inoculated roots. Phylogenetic analysis of 48 partial PAL cDNAs corresponding to 19 plant species grouped angiosperm PAL sequences into four clusters, suggesting functional differences among the six tomato genes, with PAL2 and PAL6 presumably involved in lignification, and the remaining PAL genes implicated in other biological processes. An increase in the synthesis of lignins was found 16 and 28 days after inoculation in both lines; this increase was greater and faster to develop in the resistant line. In both resistant and susceptible inoculated plants, an increase in the ratio of guaiacyl/syringyl units was detected 16 days after inoculation, resulting from the lowered amount of syringyl units in the lignins of inoculated plants.

CONCLUSIONS

The interaction between the tomato and V. dahliae triggered a number of short- and long-term defensive mechanisms. Differences were found between compatible and incompatible interactions, including onset of H2O2 production and activities of peroxidase and PAL, and phenylpropanoid metabolism and synthesis of lignins.

Comparison of transcript profiles in late blight-challenged Solanum cajamarquense and B3C1 potato clones

Two Solanum genotypes, a wild relative of cultivated potato S. cajamarquense (Cjm) and an advanced tetraploid clone B3C1 (B3), were inoculated with two Phytophthora infestans isolates and leaves were sampled at 72 and 96 h after inoculation. Gene expression in the inoculated versus noninoculated samples was monitored using the Institute of Genomic Research (TIGR) 10K potato array and real-time reverse transcriptase-polymerase chain reaction (RT-PCR). The current experiment is study number 83 of the TIGR expression profiling service project, and all data are publicly available in the Solanaceae Gene Expression Database (SGED) at ftp://ftp.tigr.org/pub/data/s_tuberosum/SGED. Differentially regulated cDNA clones were selected separately for each isolate-time point interaction by significant analysis of microarray (SAM), and differentially regulated clones were classified into functional categories by MapMan. The results show that the genes activated in B3 and Cjm have largely the same biological functions and are commonly activated when plants respond to pathogen attack. The genes activated within biological function categories were considerably different between the genotypes studied, suggesting that the defence pathways activated in B3 and Cjm during the tested conditions may involve unique genes. However, as indicated by real-time RT-PCR, some of the genes thought to be genotype specific may be activated across genotypes at other time points during disease development.

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

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

Single nucleotide polymorphisms in the allene oxide synthase 2 gene are associated with field resistance to late blight in populations of tetraploid potato cultivars

The oomycete Phytophthora infestans causes late blight, the most relevant disease of potato (Solanum tuberosum) worldwide. Field resistance to late blight is a complex trait. When potatoes are cultivated under long day conditions in temperate climates, this resistance is correlated with late plant maturity, an undesirable characteristic. Identification of natural gene variation underlying late blight resistance not compromised by late maturity will facilitate the selection of resistant cultivars and give new insight in the mechanisms controlling quantitative pathogen resistance. We tested 24 candidate loci for association with field resistance to late blight and plant maturity in a population of 184 tetraploid potato individuals. The individuals were genotyped for 230 single nucleotide polymorphisms (SNPs) and 166 microsatellite alleles. For association analysis we used a mixed model, taking into account population structure, kinship, allele substitution and interaction effects of the marker alleles at a locus with four allele doses. Nine SNPs were associated with maturity corrected resistance (P < 0.001), which collectively explained 50% of the genetic variance of this trait. A major association was found at the StAOS2 locus encoding allene oxide synthase 2, a key enzyme in the biosynthesis of jasmonates, plant hormones that function in defense signaling. This finding supports StAOS2 as being one of the factors controlling natural variation of pathogen resistance.

Characterization and differential expression analysis of artichoke phenylalanine ammonia-lyase-coding sequences

Sequences encoding phenylalanine ammonia-lyase were isolated from artichoke, by using a sequence homology strategy, by screening a genomic library and by 3'-rapid amplification of cDNA end (RACE) technology. These analyses and Southern blots suggested that, in artichoke, phenylalanine ammonia-lyase (PAL) is encoded by a small gene family. The sequences isolated from genomic DNA possess two exons and one intron at the conserved position as in most plant pal characterized to date. The 3'-RACE analysis also indicated that each member of the artichoke pal gene family was present as a pool of transcripts, different in the length of 3'-untranslated region. The deduced amino acid sequences were highly similar to those of PAL from lettuce and sunflower. One of the artichoke pal genes was completely sequenced, and its 5' upstream region contained TATA, CAAT box and cis regulatory elements identified in other phenylpropanoid pathway genes as playing a role in UV and elicitor induction. The expression of three of the identified artichoke pal sequences was evaluated in different plant parts, in developmental stages and after wounding, using gene-specific primers/probe combinations in real-time polymerase chain reaction assays. The three putative genes were differentially expressed in the plant parts analysed and were developmentally regulated. Moreover, after leaf mechanical injury, all of them were differentially regulated. The possible involvement of the single pal genes in different physiological processes is discussed.