Transcriptome analysis of Arabidopsis thaliana plants in response to kin and stranger recognition

Recent reports have demonstrated that Arabidopsis thaliana has the ability to alter its growth differentially when grown in the presence of secretions from other A. thaliana plants that are kin or strangers; however, little knowledge has been gained as to the physiological processes involved in these plant-plant interactions. Therefore, we examined the root transcriptome of A. thaliana plants exposed to stranger vs. kin secretions to determine genes involved in these processes. We conducted a whole transcriptome analysis on root tissues and categorized genes with significant changes in expression. Genes from four categories of interest based on significant changes in expression were identified as ATP/GST transporter, auxin/auxin related, secondary metabolite and pathogen response genes. Multiple genes in each category were tested and results indicated that pathogen response genes were involved in the kin recognition response. Plants were then infected with Pseudomonas syringe pv. Tomato DC3000 to further examine the role of these genes in plants exposed to own, kin and stranger secretions in pathogen resistance. This study concluded that multiple physiological pathways are involved in the kin recognition. The possible implication of this study opens up a new dialog in terms of how plant-plant interactions change under a biotic stress

Cyanogenic pseudomonads influence multitrophic interactions in the rhizosphere.

In the rhizosphere, plant roots cope with both pathogenic and beneficial bacterial interactions. The exometabolite production in certain bacterial species may regulate root growth and other root-microbe interactions in the rhizosphere. Here, we elucidated the role of cyanide production in pseudomonad virulence affecting plant root growth and other rhizospheric processes. Exposure of Arabidopsis thaliana Col-0 seedlings to both direct (with KCN) and indirect forms of cyanide from different pseudomonad strains caused significant inhibition of primary root growth. Further, we report that this growth inhibition was caused by the suppression of an auxin responsive gene, specifically at the root tip region by pseudomonad cyanogenesis. Additionally, pseudomonad cyanogenesis also affected other beneficial rhizospheric processes such as Bacillus subtilis colonization by biofilm formation on A. thaliana Col-0 roots. The effect of cyanogenesis on B. subtilis biofilm formation was further established by the down regulation of important B. subtilis biofilm operons epsA and yqxM. Our results show, the functional significance of pseudomonad cyanogenesis in regulating multitrophic rhizospheric interactions

Direct and indirect effect of different doses (0–700 µM) cyanide on the growth of <i>A. thaliana</i> Col-0 seedling.

<p>The data shows the linear regression plots (A&B) shows the predicted (line) and experimental (dots) values of primary root length at different concentrations of KCN(B; <i>r</i>² = 0.8581) and HCN (D; <i>r</i>² = 0.779). Data is the mean±SD of 12 replicates and the experiment was repeated on two independent occasions.</p

Suppression of <i>B. subtilis</i> biofilm formation on <i>A. thaliana</i> Col-0 roots by indirect exposure of the pseudomonad strains and cyanide (A) and the effect of indirect exposure of the pseudomonad strains and cyanide on single cell growth of <i>B. subtilis</i> (B).

<p>The images show complete suppression of <i>B. subtilis</i> biofilm formation when exposed to the indirect exposure of the strains PAO1, PA14, CHAO and HCN when compared to control plants not exposed to either bacterial culture or HCN and Δ<i>hcnB</i> mutants PAO6344 and CHAO77. The data also shows extensive colonization and biofilm formation by <i>B. subtilis</i> with indirect bacterial exposure from the <i>hcnB</i> mutants PAO6344 and CHAO77. The images were representative of the roots from six independent plants imaged.</p

Kinetics of cyanide synthesis and accumulation in the different pseudomonad strains.

<p>The data shows highest cyanide accumulation in CHAO and PAO1 with an increased synthesis during late log phase and early stationary phase. The data is the mean±SD of 3 replicates and the experiment was repeated on two independent occasions.</p

Effect of indirect exposure of the pseudomonad strains and cyanide on the transcription of the <i>yqxM</i> operon in <i>B. subtilis.</i>

<p>Strain <i>Marburg thrC</i>::<i>yqxM</i>-<i>lacZ</i> (NRS1531) was grown in biofilm medium under biofilm formation conditions at 37°C with or without exposure to pseudomonad strains and HCN. Growth (A) and β-galactosidase activity (B) were measured at regular intervals and plotted as a function of time. These experiments were repeated on at least 3 independent occasions and a representative plot is shown. Data is the mean±SD of 12 replicates and the experiment was repeated on two independent occasions.</p