Systemic resistance and lipoxygenase-related defence response induced in tomato by Pseudomonas putida strain BTP1

BACKGROUND: Previous studies showed the ability of Pseudomonas putida strain BTP1 to promote induced systemic resistance (ISR) in different host plants. Since ISR is long-lasting and not conducive for development of resistance of the targeted pathogen, this phenomenon can take part of disease control strategies. However, in spite of the numerous examples of ISR induced by PGPR in plants, only a few biochemical studies have associated the protective effect with specific host metabolic changes. RESULTS: In this study, we showed the protective effect of this bacterium in tomato against Botrytis cinerea. Following treatment by P. putida BTP1, analyses of acid-hydrolyzed leaf extracts showed an accumulation of antifungal material after pathogen infection. The fungitoxic compounds thus mainly accumulate as conjugates from which active aglycones may be liberated through the activity of hydrolytic enzymes. These results suggest that strain BTP1 can elicit systemic phytoalexin accumulation in tomato as one defence mechanism. On another hand, we have shown that key enzymes of the lipoxygenase pathway are stimulated in plants treated with the bacteria as compared with control plants. Interestingly, this stimulation is observed only after pathogen challenge in agreement with the priming concept almost invariably associated with the ISR phenomenon. CONCLUSION: Through the demonstration of phytoalexin accumulation and LOX pathway stimulation in tomato, this work provides new insights into the diversity of defence mechanisms that are inducible by non-pathogenic bacteria in the context of ISR

Co-Evolution of Mitochondrial tRNA Import and Codon Usage Determines Translational Efficiency in the Green Alga Chlamydomonas

Mitochondria from diverse phyla, including protozoa, fungi, higher plants, and humans, import tRNAs from the cytosol in order to ensure proper mitochondrial translation. Despite the broad occurrence of this process, our understanding of tRNA import mechanisms is fragmentary, and crucial questions about their regulation remain unanswered. In the unicellular green alga Chlamydomonas, a precise correlation was found between the mitochondrial codon usage and the nature and amount of imported tRNAs. This led to the hypothesis that tRNA import might be a dynamic process able to adapt to the mitochondrial genome content. By manipulating the Chlamydomonas mitochondrial genome, we introduced point mutations in order to modify its codon usage. We find that the codon usage modification results in reduced levels of mitochondrial translation as well as in subsequent decreased levels and activities of respiratory complexes. These effects are linked to the consequential limitations of the pool of tRNAs in mitochondria. This indicates that tRNA mitochondrial import cannot be rapidly regulated in response to a novel genetic context and thus does not appear to be a dynamic process. It rather suggests that the steady-state levels of imported tRNAs in mitochondria result from a co-evolutive adaptation between the tRNA import mechanism and the requirements of the mitochondrial translation machinery

Correction: Co-Evolution of Mitochondrial tRNA Import and Codon Usage Determines Translational Efficiency in the Green Alga Chlamydomonas.

[This corrects the article DOI: 10.1371/journal.pgen.1002946.]

Respiratory enzyme activities of T11-10, T11-10/2, and T22-11 transformants.

<p>Respiratory activities were measured on membrane fractions of T11-10, T11-10/2 and T22-11 mutants. NADH:Duroquinone corresponds to the rotenone-sensitive NADH:duroquinone oxidoreductase activity (nmol of NADH oxidized min⁻¹ mg of proteins⁻¹); NADH:Ferricyanide corresponds to the NADH:Fe(CN)₆³⁻ oxidoreductase activity (nmol of K3Fe(CN)₆³⁻ reduced min⁻¹ mg of proteins⁻¹); CII+III corresponds to the succinate:cytochrome <i>c</i> oxidoreductase activity (nmol cytochrome <i>c</i> reduced min⁻¹ mg of proteins⁻¹); CIV corresponds to the cytochrome <i>c</i> oxidase activity (nmol of cytochrome <i>c</i> oxidized min⁻¹ mg of proteins⁻¹). Asterisks indicate statistically significantly differences using Student <i>t</i> test with a significance threshold of 0.05. <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1002946#s2" target="_blank">Results</a> are means of 3 to 6 independent experiments.</p

Total respiration and doubling time in T11-10, T11-10/2, and T22-11 transformants.

<p>Dark whole-cell respiratory rates are expressed in nmol of O₂ min⁻¹ 10⁻⁷ cells ± SD (mean of 3 independent experiments). Doubling times were measured in heterotrophic conditions (D) and mixotrophic conditions (L) and are expressed in hours ± SD (mean of 3 independent experiments). Asterisks indicate statistically significantly differences using Student <i>t</i> test with a significance threshold of 0.05.</p

Molecular characterization of the transformants.

<p>(A) Schematic map of the <i>Chlamydomonas reinhardtii</i> mitochondrial genome. Boxes represent protein-coding genes: (<i>cob</i>) apocytochrome <i>b</i> of complex III; (<i>nd1</i>, <i>2</i>, <i>4</i>, <i>5</i> and <i>6</i>) subunits of complex I; (<i>cox1</i>) subunit 1 of complex IV; (<i>rtl</i>) reverse transcriptase-like protein. W, Q, and M represent tRNAs for Trp, Glu, and Met, respectively. The bidirectional origin of transcription between <i>nd5</i> and <i>cox1</i> genes is represented by a dashed vertical line and two horizontal arrows. Terminal inverted repeats are shown by short arrows and <i>Sac</i>I digestion site at position 5.5 kb (GenBank u03843 numbering) is indicated. Region where modifications on the <i>nd4</i> gene were found on T11-10, T11-10/2 and T22-11 transformants is indicated in grey. Position and name of primers are indicated above the map. Primers with a star are specific for the modified gene version (for primer sequence see <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1002946#pgen.1002946.s004" target="_blank">Table S1</a>). Positions of the <i>dum11</i> and <i>dum22</i> deletions are shown. Mitochondrial DNA fragments contained in pND4-LP, pCucob and pCumut are schematized. Grey boxes represent the modified genes where GGC/GGT codons were changed in GGG codons. (B) Detection of the <i>cob</i> gene in transformants obtained after biolistic transformation with pND4-LP (T-ND4-LP) and pCucob (T-cucob) constructs. PCR analyses were performed with cobF/cobR (1) and telF/cobR (2) pair primers. (C) Detection of the mutated and the wild-type <i>nd4</i> genes on T11-10, T11-10/2 and T22-11 transformants. PCR analyses were performed with 4F2*/4R2 and 4F2/4R2 pair primers for the modified <i>nd4</i> gene (<i>nd4*</i>) and for wild-type <i>nd4</i> gene (<i>nd4</i>) respectively. (D–E) Reconstitution of complete mitochondrial genome in T11-10, T11-10/2 and T22-11 transformants. Southern blot analyses were performed (D) on total DNA with the <i>nd6</i> PCR probe and (E) on <i>Sac</i>I digested DNA with <i>nd4</i> and <i>nd6</i> PCR probes. (F) Transcript levels of <i>nd4</i> and <i>nd6</i> genes in T11-10, T11-10/2 and T22-11 transformants. Northern blot analyses were performed on total RNA with <i>nd4</i> and <i>nd6</i> PCR probes. Loadings of rRNAs are shown.</p

Analysis of the import status of mitochondrial tRNAs in T22-11 transformant.

<p>(A) Northern blot analysis of mitochondrial tRNAs extracted from the T22-WT strain and T22-11 transformant. Hybridizations were performed with radiolabeled oligonucleotides specific for cytosolic tRNA^Gly(GCC) (G1), tRNA^Gly(UCC) (G2), tRNA^Gly(CCC) (G3), tRNA^Val(AAC) (V) and tRNA^Leu(AAG) (L); for mitochondrial tRNA^Met (M mt), tRNA^Gln (Q mt) and for the mitochondrial L3a rRNA (L3a mt). (B) Signals were quantified and normalized with the L3a mt signal. <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1002946#s2" target="_blank">Results</a> are the means of 3 to 5 independent experiments and correspond to the percentage of variation of tRNA steady-state levels in the T22-11 transformant as compared to the T22-WT strain. Asterisks indicate statistically significant differences using Student <i>t</i> test with a significance threshold of 0.05.</p