Proteomics fingerprinting reveals importance of iron and oxidative stress in - interactions.

INTRODUCTION

The Gram-positive actinobacterium is the major causal agent of potato common scab. The main pathogenicity factor is thaxtomin A, a phytotoxin that causes atypical cell death, although other secondary metabolites have been described to play a role in virulence. Despite this, many aspects of the interaction between and its primary host L. remain to be elucidated.

METHODS

Intracellular proteins of EF-35 grown in the presence of produced tubers (microtubers) of the Russet Burbank and Yukon Gold potato cultivars were extracted and analysed by electrospray mass spectrometry (ES MS/MS). Based on the results of proteomic analysis, iron quantification by ICP-MS and nitrite quantification using Griess reagent in growth media as well as RT-qPCR analysis of the siderophore pyochelin gene expression were performed in the presence and absence of microtubers. Hydrogen peroxide accumulation was also determined in the nutrient medium used for co-cultivation of bacteria and potato microtubers.

RESULTS

Potato microtubers caused an increase in the content of bacterial proteins involved in stress and defense, secondary metabolism, and cell differentiation, as well as secreted proteins. Co-cultivation with potato microtubers induced the accumulation of proteins implicated in siderophore pyochelin biosynthesis, nitrite production and oxidative stress perception and response. The increase in the abundance of proteins related to pyochelin biosynthesis was consistent with a significant decrease in the iron content in the culture medium, as well as with induction of expression of pyochelin biosynthesis genes. Elevated nitrite/sulfite reductase protein levels were associated with increased nitrite excretion by cells in the presence of host microtubers. The increase in the levels of proteins associated with signaling and oxidative stress response could have been caused by the accumulation of ROS, in particular hydrogen peroxide, detected in the studied system.

DISCUSSION

These findings show that interactions of with living potato microtubers induce the production of secondary metabolites, defense responses, and protection from oxidative stress. This study suggests the importance of iron during host - interactions, resulting in competition between pathogen and its host.