Enhancement of the plant innate immunity as a means to reduce Salmonella colonization in plants

The aim of the present study was to examine whether improvement of plant innate immunity is capable of restricting Salmonella colonization in plants. To this purpose, we examined whether potential PAMPs are capable of limiting Salmonella growth on plant surfaces either by exogenous application to tobacco leaves or by transient expression via Agrobacterium. Preliminary results showing the effectiveness of both methods in restricting Salmonella colonization will be presented

Hydroponic Common-Bean Performance under Reduced N-Supply Level and Rhizobia Application

This study aims to explore the possibility of a reduced application of inorganic nitrogen (N) fertiliser on the yield, yield qualities, and biological nitrogen fixation (BNF) of the hydroponic common bean (Phaseolus vulgaris L.), without compromising plant performance, by utilizing the inherent ability of this plant to symbiotically fix N-2. Until the flowering stage, plants were supplied with a nutrient solution containing N-concentrations of either a, 100%, conventional standard-practice, 13.8 mM; b, 75% of the standard, 10.35 mM; or c, 50% of the standard, 6.9 mM. During the subsequent reproductive stage, inorganic-N treatments b and c were decreased to 25% of the standard, and the standard (100% level) N-application was not altered. The three different inorganic-N supply treatments were combined with two different rhizobia strains, and a control (no-inoculation) treatment, in a two-factorial experiment. The rhizobia strains applied were either the indigenous strain Rhizobium sophoriradicis PVTN21 or the commercially supplied Rhizobium tropici CIAT 899. Results showed that the 50-25% mineral-N application regime led to significant increases in nodulation, BNF, and fresh-pod yield, compared to the other treatment, with a reduced inorganic-N supply. On the other hand, the 75-25% mineral-N regime applied during the vegetative stage restricted nodulation and BNF, thus incurring significant yield losses. Both rhizobia strains stimulated nodulation and BNF. However, the BNF capacity they facilitated was suppressed as the inorganic-N input increased. In addition, strain PVTN21 was superior to CIAT 899-as 50-25% N-treated plants inoculated with the former showed a yield loss of 11%, compared to the 100%-N-treated plants. In conclusion, N-use efficiency optimises BNF, reduces mineral-N-input dependency, and therefore may reduce any consequential negative environmental consequences of mineral-N over-application

Commonalities and differences of T3SSs in rhizobia and plant pathogenic bacteria

Plant pathogenic bacteria and rhizobia infect higher plants albeit the interactions with their hosts are principally distinct and lead to completely different phenotypic outcomes, either pathogenic or mutualistic, respectively. Bacterial protein delivery to plant host plays an essential role in determining the phenotypic outcome of plant-bacteria interactions. The involvement of type III secretion systems (T3SSs) in mediating animal- and plant-pathogen interactions was discovered in the mid-80’s and is now recognized as a multiprotein nanomachine dedicated to trans-kingdom movement of effector proteins. The discovery of T3SS in bacteria with symbiotic lifestyles broadened its role beyond virulence. In most T3SS-positive bacterial pathogens, virulence is largely dependent on functional T3SSs, while in rhizobia the system is dispensable for nodulation and can affect positively or negatively the mutualistic associations with their hosts. This review focuses on recent comparative genome analyses in plant pathogens and rhizobia that uncovered similarities and variations among T3SSs in their genetic organization, regulatory networks and type III secreted proteins and discusses the evolutionary adaptations of T3SSs and type III secreted proteins that might account for the distinguishable phenotypes and host range characteristics of plant pathogens and symbionts

Characterization of the biocontrol activity of pseudomonas fluorescens strain X reveals novel genes regulated by glucose.

Pseudomonas fluorescens strain X, a bacterial isolate from the rhizosphere of bean seedlings, has the ability to suppress damping-off caused by the oomycete Pythium ultimum. To determine the genes controlling the biocontrol activity of strain X, transposon mutagenesis, sequencing and complementation was performed. Results indicate that, biocontrol ability of this isolate is attributed to gcd gene encoding glucose dehydrogenase, genes encoding its co-enzyme pyrroloquinoline quinone (PQQ), and two genes (sup5 and sup6) which seem to be organized in a putative operon. This operon (named supX) consists of five genes, one of which encodes a non-ribosomal peptide synthase. A unique binding site for a GntR-type transcriptional factor is localized upstream of the supX putative operon. Synteny comparison of the genes in supX revealed that they are common in the genus Pseudomonas, but with a low degree of similarity. supX shows high similarity only to the mangotoxin operon of Ps. syringae pv. syringae UMAF0158. Quantitative real-time PCR analysis indicated that transcription of supX is strongly reduced in the gcd and PQQ-minus mutants of Ps. fluorescens strain X. On the contrary, transcription of supX in the wild type is enhanced by glucose and transcription levels that appear to be higher during the stationary phase. Gcd, which uses PQQ as a cofactor, catalyses the oxidation of glucose to gluconic acid, which controls the activity of the GntR family of transcriptional factors. The genes in the supX putative operon have not been implicated before in the biocontrol of plant pathogens by pseudomonads. They are involved in the biosynthesis of an antimicrobial compound by Ps. fluorescens strain X and their transcription is controlled by glucose, possibly through the activity of a GntR-type transcriptional factor binding upstream of this putative operon

High level resistance against rhizomania disease by simultaneously integrating two distinct defense mechanisms.

With the aim of achieving durable resistance against rhizomania disease of sugar beet, the employment of different sources of resistance to Beet necrotic yellow vein virus was pursued. To this purpose, Nicotiana benthamiana transgenic plants that simultaneously produce dsRNA originating from a conserved region of the BNYVV replicase gene and the HrpZ(Psph) protein in a secreted form (SP/HrpZ(Psph)) were produced. The integration and expression of both transgenes as well as proper production of the harpin protein were verified in all primary transformants and selfed progeny (T1, T2). Transgenic resistance was assessed by BNYVV-challenge inoculation on T2 progeny by scoring disease symptoms and DAS-ELISA at 20 and 30 dpi. Transgenic lines possessing single transformation events for both transgenes as well as wild type plants were included in inoculation experiments. Transgenic plants were highly resistant to virus infection, whereas in some cases immunity was achieved. In all cases, the resistant phenotype of transgenic plants carrying both transgenes was superior in comparison with the ones carrying a single transgene. Collectively, our findings demonstrate, for a first time, that the combination of two entirely different resistance mechanisms provide high level resistance or even immunity against the virus. Such a novel approach is anticipated to prevent a rapid virus adaptation that could potentially lead to the emergence of isolates with resistance breaking properties

Arrangement of the genes in the genomic locus of <i>sup</i>5 and <i>sup</i>6, compared to other <i>Pseudomonas</i> strains, and complementation analysis of the region.

<p>The lines beneath the genomic of <i>Ps. fluorescens</i> X represent regions of this locus that were PCR-amplified, cloned into pBBR1MCS5 and tested for complementation. Ability to complement is noted with plus (+) or minus (−). Putative ORFs are indicated by thick coloured arrows on a line. Genes that might be organised in a putative operon are enclosed by a grey frame. The direction of the plasposon Tn<i>5</i>-RL27 insertion in mutants δ40 and ρ93 is indicated with a black arrow beneath the sequence (▸). Predicted sites for the unique putative promoter and operator are also marked (;). Size, genomic location and locus tag of the different ORFs sequenced in <i>Ps. aeruginosa</i> PA7, <i>Ps. fluorescens</i> Pf0–1, <i>Ps. fluorescens</i> SBW25, <i>Ps. entomophila</i> L48, <i>Ps. syringae</i> pv. <i>syringae</i> B728a,<i>Ps. syringae</i> pv. <i>tomato</i> DC3000 and <i>Ps. syringae</i> pv. <i>syringae</i> UMAF0158 are indicated.</p

RT-PCR amplification products obtained from transgenic <i>N. benthamiana</i> plants expressing the BNYVV replicase-derived transgene.

<p>Lane M: Marker in bp (Gene Ruler Ladder mix, Fermentas). Lanes 1, 2, 3: Representative T2 double transgenic plants, expressing the <i>hrpZ_Psph</i> and the BNYVV replicase-derived transgenes, presenting high, moderate and low resistance levels, respectively. Lanes 4, 5, 6: Representative T2 GW-IR3-transformed plants presenting high, moderate and low resistance levels, respectively. The <i>EF1a</i> gene transcript is used as loading control for equal amounts of RNA.</p

Characteristics of sup⁻ mutants and complementation analysis.

<p>ND: Not Detected.</p>a<p>Acidification was observed on solid minimal medium M9 supplemented with 2% w/v glucose, as described before <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061808#pone.0061808-Pujol1" target="_blank">[14]</a>.</p>b<p>Enzyme treatment was performed for filtrates from incubation in PDB, as described before <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061808#pone.0061808-Arrebola2" target="_blank">[47]</a>.</p