Apoplast, Apoplast! Which Apoplast Do You Like?- Biochemically Altered Apoplasts in Tomato for Xanthomonas and Pseudomonas

Abstract

Plants are often exposed to pathogens that biochemically alter leaf niches, such as the apoplast, the intercellular space filled with gas or water. Two such pathogens of tomato are Pseudomonas syringae pv. tomato (Pst) and Xanthomonas hortorum gardneri (Xg). Both bacteria cause symptoms that appear macroscopically similar, but they have been observed to differentially manipulate the stomata, gas exchange pores in leaves that allow bacteria access to the apoplast from the leaf surface. We found that there is a difference in metabolites of Pst- versus Xg- infected leaves, suggesting different biochemical alterations within the plant during Pst and Xg infection. To further understand the differences these bacteria cause to leaves, we investigated whether an apoplast that has been biochemically altered by the one pathogen may impact the growth of the other pathogen, compared to their growth in a healthy apoplast. We found that Xg showed a higher growth rate in any infected apoplasts, while Pst showed a higher growth rate in healthy apoplasts and almost no growth in the infected apoplasts with some replicates showing growth rates between 0 to 0.025. We hypothesize that leaf infection releases unique metabolites compared to a healthy plant that increases Xg growth.