The Detriment of Salicylic Acid to the Pseudomonas savastanoi pv. phaseolicola Proteome

Indole Alkaloid Production by the Halo Blight Bacterium Treated with the Phytoalexin Genistein

When Pseudomonas savastanoi pv. phaseolicola, the bacterium that causes halo blight, induces hypersensitive immunity in common bean leaves, salicylic acid and phytoalexins accumulate at the site of infection. Both salicylic acid and the phytoalexin resveratrol exert antibiotic activities and toxicities in vitro, adversely disrupting the P. savastanoi pv. phaseolicola proteome and metabolism and stalling replication and motility. These efficacious properties likely contribute to the cessation of bacterial spread in beans. Genistein is an isoflavonoid phytoalexin that also accumulates during bean immunity, so we tested its antibiotic potential in vitro. Quantitative proteomics revealed that genistein did not induce proteomic changes in P. savastanoi pv. phaseolicola in the same way that salicylic acid or resveratrol did. Rather, a dioxygenase that could function to metabolize genistein was among the most highly induced enzymes. Indeed, high-throughput metabolomics provided direct evidence for genistein catabolism. Metabolomics also revealed that genistein induced the bacterium to produce indole compounds, several of which had structural similarity to auxin. Additional mass spectrometry analyses proved that the bacterium produced an isomer of the auxin indole-3-acetic acid but not indole-3-acetic acid proper. These results reveal that P. savastanoi pv. phaseolicola can tolerate bean genistein and that the bacterium likely responds to bean-produced genistein during infection, using it as a signal to increase pathogenicity, possibly by altering host cell physiology or metabolism through the production of potential auxin mimics.

Editing Metabolism, Sex, and Microbiome: How Can We Help Poplar Resist Pathogens?

Poplar (Populus) is a genus of woody plants of great economic value. Due to the growing economic importance of poplar, there is a need to ensure its stable growth by increasing its resistance to pathogens. Genetic engineering can create organisms with improved traits faster than traditional methods, and with the development of CRISPR/Cas-based genome editing systems, scientists have a new highly effective tool for creating valuable genotypes. In this review, we summarize the latest research data on poplar diseases, the biology of their pathogens and how these plants resist pathogens. In the final section, we propose to plant male or mixed poplar populations; consider the genes of the MLO group, transcription factors of the WRKY and MYB families and defensive proteins BbChit1, LJAMP2, MsrA2 and PtDef as the most promising targets for genetic engineering; and also pay attention to the possibility of microbiome engineering.

How plants manage pathogen infection

To combat microbial pathogens, plants have evolved specific immune responses that can be divided into three essential steps: microbial recognition by immune receptors, signal transduction within plant cells, and immune execution directly suppressing pathogens. During the past three decades, many plant immune receptors and signaling components and their mode of action have been revealed, markedly advancing our understanding of the first two steps. Activation of immune signaling results in physical and chemical actions that actually stop pathogen infection. Nevertheless, this third step of plant immunity is under explored. In addition to immune execution by plants, recent evidence suggests that the plant microbiota, which is considered an additional layer of the plant immune system, also plays a critical role in direct pathogen suppression. In this review, we summarize the current understanding of how plant immunity as well as microbiota control pathogen growth and behavior and highlight outstanding questions that need to be answered.

Disruptive Effects of Resveratrol on a Bacterial Pathogen of Beans

Upon inoculation, common beans immune to Pseudomonas savastanoi pv phaseolicola race 5 (R5) accumulate resveratrol, a phytoalexin. How resveratrol acts upon on this bacterium is not known, although in animal pathogenic bacteria in vitro resveratrol reduces ATPase (ATP = adenosine triphosphate) activity, cellular motility, quorum sensing, and biofilm formation. In this study, mass spectrometry was used to monitor the effects of resveratrol on R5. R5 responded by producing multidrug efflux proteins to pump resveratrol out of cells. Changes in R5 enzyme abundances were consistent with a slowed tricarboxylic acid cycle, the consequence of which likely impeded ATP production by oxidative phosphorylation. There also were enzymatic shifts consistent with decreased amounts of flagellar proteins and decreased pools of purines. A motility assay confirmed a reduction in R5 flagellar movement in resveratrol, and mass spectrometry of metabolite extracts confirmed decreased pools of guanosine 5'-monophosphate and adenosine 5'-monophosphate. Mass spectrometry also detected the accumulation of a reactive aldehyde byproduct of resveratrol catabolism. Overall, the study reveals that resveratrol likely imparts its antibiotic activity during plant immunity by disturbing the bacterial tricarboxylic acid cycle, interfering with ATP biosynthesis at the electron transport chain, and by decreasing bacterial proteins needed for pathogenicity and leaf colonization. Mass spectrometry data files for this study can be retrieved from massive.ucsd.edu (MSV000090171 and MSV000090172).