Proteomic analysis of glucohexaose induced resistance to downy mildew in Cucumis sativus

Glucohexaose, as one of synthetic oligosaccharides, induces the resistance response to protect plants from pathogen infection by inducing the systemic acquired resistance-like (SAR-like) response. To study the molecular mechanism of glucohexaose induced resistance, we investigate the physiological, biochemical and proteomic changes after glucohexaose treatment. The results shows cucumber plants had the highest protection level of 66.79% 48 h after the third times of 10 μg mLglucohexaose treatment. Significant increases in chlorophyll, photo synthetic rate, soluble sugar, leave dry weight and HO were observed after glucohexaose treatment. Eighteen up-regulated proteins were identified by MALDI-TOF/TOF in glucohexaose-treated plants, predicted to be involved in photosynthesis, photorespiration, oxidative burst, transcriptional regulation, signal transduction and pathogen defense processes. The identification of up-regulated proteins involved in photo synthetic processes is a significant finding which suggests that a boost in metabolites is required for repartition of resources towards defense mechanisms. The proteins which responded to glucohexaose also included those associated with oxidative burst response, such as APX and isocitrate dehydrogenase. More comprehensive studies about the link between the molecular mechanisms regulated by ROS mediated photosynthesis and cucumber induced resistance by glucohexaose, are necessary in the future to broaden our understanding of induced resistance in plants

Signaling Specificity Provided by the Arabidopsis thaliana Heterotrimeric G-Protein γ Subunits AGG1 and AGG2 Is Partially but Not Exclusively Provided through Transcriptional Regulation

The heterotrimeric G-protein complex in Arabidopsis thaliana consists of one α, one ß and three γ subunits. While two of the γ subunits, AGG1 and AGG2 have been shown to provide functional selectivity to the Gßγ dimer in Arabidopsis, it is unclear if such selectivity is embedded in their molecular structures or conferred by the different expression patterns observed in both subunits. In order to study the molecular basis for such selectivity we tested genetic complementation of AGG1- and AGG2 driven by the respectively swapped gene promoters. When expressed in the same tissues as AGG1, AGG2 rescues some agg1 mutant phenotypes such as the hypersensitivity to Fusarium oxysporum and D-mannitol as well as the altered levels of lateral roots, but does not rescue the early flowering phenotype. Similarly, AGG1 when expressed in the same tissues as AGG2 rescues the osmotic stress and lateral-root phenotypes observed in agg2 mutants but failed to rescue the heat-stress induction of flowering. The fact that AGG1 and AGG2 are functionally interchangeable in some pathways implies that, at least for those pathways, signaling specificity resides in the distinctive spatiotemporal expression patterns exhibited by each γ subunit. On the other hand, the lack of complementation for some phenotypes indicates that there are pathways in which signaling specificity is provided by differences in the primary AGG1 and AGG2 amino acid sequences

G gamma 1+G gamma 2+G gamma 3=G beta: The search for heterotrimeric G-protein gamma subunits in Arabidopsis is over

In Arabidopsis, heterotrimeric G-proteins consist of one Get (GPA1), one G beta (AGB1) and three G gamma (AGG1, AGG2 and AGG3) subunits. G beta and G gamma subunits function as obligate heterodimers, therefore any phenotypes observed in G beta-deficient mutants should be apparent in Goy-deficient mutants. Nevertheless, the first two G gamma subunits discovered failed to explain many of the phenotypes shown by the agb1 mutants in Arabidopsis, prompting the search for additional G gamma subunits. The recent discovery of an additional, although quite atypical, G gamma subunit in Arabidopsis (AGG3) has helped to complete the picture and explains almost all of the missing agb1 'orphan' phenotypes. There is nevertheless still one unexplained phenotype, the reduction in rosette size reported for agb1, that has not been observed in any of the individual agg mutants or the double agg1 agg2 mutant. We have now created a triple gamma mutant (agg1agg2agg3) in Arabidopsis and show that it recapitulates the remaining 'orphan' agb1 phenotypes. Triple agg1agg2agg3 mutants show the reduction in rosette size previously observed in agb1 mutants. In addition we show that small differences in flower and silique size observed between agb1 and agg3 mutants are also accounted for by the triple agg1agg2agg3 mutant. Our results strongly suggest that there are no additional members of the G-protein family remaining to be discovered in Arabidopsis. (C) 2011 Elsevier GmbH. All rights reserved

<i>AGG1</i> complements some but not all <i>agg2</i> mutant phenotypes.

<p>(A) Germination dynamics of wild-type, mutant and complementation lines on 0.5x MS supplemented with 6% D-mannitol during 9 days after stratification. Each genotype was analyzed in three replica plates with more than 100 seeds. Insert shows control germination without D-mannitol. (B) Percentage of germinated seeds at day 3 from panel (A) demonstrating highest difference between genotypes. Bars represent average value of three replicates (more than 100 seeds each). Error bars show standard errors. Letters indicate groups with statistically significant differences in seed germination (P<0.05, one-way ANOVA). (C) Total number of lateral roots was scored in two-week-old seedlings grown vertically on 0.5x MS supplemented with 1% sucrose. Bars represent average values ±SE of 15 plants per genotype. Letters indicate groups with statistically significant differences in number of lateral roots (P<0.05, one-way ANOVA). (D, E) <i>AGG1</i> failed to complement the <i>agg2-1</i> mutant on high temperature-induced flowering. (D) Effect of the <i>agg2-1</i> mutation on high temperature-induced flowering. Col-0 and <i>agg2-1</i> plants were initially grown at 22°C for two weeks and then divided into two groups: the first group was kept at 22°C, while the second group was transferred to 29°C. Day of inflorescence appearance was recorded for at least 30 plants of each genotype. Bars represent the average number of days from germination till inflorescence appearance ± SE. Letters indicate groups with statistically significant differences (P<0.05, one-way ANOVA). (E) Average number of days from germination till inflorescence appearance in at least 30 plants of each genotype induced at 29°C. Bars represent the average number of days from germination till inflorescence appearance ± SE. Letters indicate groups with statistically significant differences (P<0.05, one-way ANOVA).</p

Summary of Gγ1 and Gγ2 complementation studies.

<p>Summary of Gγ1 and Gγ2 complementation studies.</p

AGG2 complements some but not all <i>agg1</i> mutant phenotypes.

<p>(A) Sensitivity to <i>F. oxysporum</i>. Roots of two-week-old seedlings were inoculated with <i>F. oxysporum</i> spores and total number and number of chlorotic leaves were counted 9 days after inoculation for each plant. The ratio of chlorotic/total number of leaves was used to evaluate disease progression in infected plants. Bars on the graph represent average values estimated for 20 plants per each genotype. Error bars show standard errors. Letters indicate groups with statistically significant differences in disease progression (P<0.05, one-way ANOVA). (B) Total number of lateral roots was scored in two-week-old seedlings grown vertically on 0.5x MS supplemented with 1% sucrose. Bars represent average values ±SE of 15 plants per genotype. Letters indicate groups with statistically significant differences in number of lateral roots (P<0.05, one-way ANOVA). (C) Adventitious root development in excised hypocotyls was induced by supplementing media with 1µM NAA. Photos of representative hypocotyls from each tested genotype are shown. (D) Germination dynamics of wild-type, mutant and complementation lines grown on 0.5x MS supplemented with 6% D-mannitol during 8 days after stratification. Each genotype was analyzed in three replica plates with more than 100 seeds. Insert shows control germination without D-mannitol. (E) Percentage of germinated seeds at day 8 from panel (D) showing the highest difference between genotypes. Bars represent average value of three replicates (more than 100 seeds each). Error bars show standard errors. Letters indicate groups with statistically significant differences in seed germination (P<0.05, one-way ANOVA). (F) AGG2 partial rescue of the early flowering phenotype observed in <i>agg1-1c</i> mutants. Plants were grown under long day conditions (16 h light/8 h dark) at 23°C. Day of inflorescence appearance was recorded for at least 30 plants of each genotype. Bars represent average number of days from germination till inflorescence appearance ± SE. Letters indicate groups with statistically significant differences (P<0.05, one-way ANOVA).</p

Quorum-Sensing Regulation of Adhesion in Serratia marcescens MG1 Is Surface Dependent

Serratia marcescens is an opportunistic pathogen and a major cause of ocular infections. In previous studies of S. marcescens MG1, we showed that biofilm maturation and sloughing were regulated by N-acyl homoserine lactone (AHL)-based quorum sensing (QS). Because of the importance of adhesion in initiating biofilm formation and infection, the primary goal of this study was to determine whether QS is important in adhesion to both abiotic and biotic surfaces, as assessed by determining the degree of attachment to hydrophilic tissue culture plates and human corneal epithelial (HCE) cells. Our results demonstrate that while adhesion to the abiotic surface was AHL regulated, adhesion to the HCE cell biotic surface was not. Type I fimbriae were identified as the critical adhesin for non-QS-mediated attachment to the biotic HCE cell surface but played no role in adhesion to the abiotic surface. While we were not able to identify a single QS-regulated adhesin essential for attachment to the abiotic surface, four AHL-regulated genes involved in adhesion to the abiotic surface were identified. Interestingly, two of these genes, bsmA and bsmB, were also shown to be involved in adhesion to the biotic surface in a non-QS-controlled fashion. Therefore, the expression of these two genes appears to be cocontrolled by regulators other than the QS system for mediation of attachment to HCE cells. We also found that QS in S. marcescens regulates other potential cell surface adhesins, including exopolysaccharide and the outer membrane protein OmpX. We concluded that S. marcescens MG1 utilizes different regulatory systems and adhesins in attachment to biotic and abiotic surfaces and that QS is a main regulatory pathway in adhesion to an abiotic surface but not in adhesion to a biotic surface

Signaling Specificity Provided by the Arabidopsis thaliana Heterotrimeric G-Protein γ Subunits AGG1 and AGG2 Is Partially but Not Exclusively Provided through Transcriptional Regulation

The heterotrimeric G-protein complex in Arabidopsis thaliana consists of one α, one ß and three γ subunits. While two of the γ subunits, AGG1 and AGG2 have been shown to provide functional selectivity to the Gßγ dimer in Arabidopsis, it is unclear if such selectivity is embedded in their molecular structures or conferred by the different expression patterns observed in both subunits. In order to study the molecular basis for such selectivity we tested genetic complementation of AGG1- and AGG2 driven by the respectively swapped gene promoters. When expressed in the same tissues as AGG1, AGG2 rescues some agg1 mutant phenotypes such as the hypersensitivity to Fusarium oxysporum and D-mannitol as well as the altered levels of lateral roots, but does not rescue the early flowering phenotype. Similarly, AGG1 when expressed in the same tissues as AGG2 rescues the osmotic stress and lateral-root phenotypes observed in agg2 mutants but failed to rescue the heat-stress induction of flowering. The fact that AGG1 and AGG2 are functionally interchangeable in some pathways implies that, at least for those pathways, signaling specificity resides in the distinctive spatiotemporal expression patterns exhibited by each γ subunit. On the other hand, the lack of complementation for some phenotypes indicates that there are pathways in which signaling specificity is provided by differences in the primary AGG1 and AGG2 amino acid sequences