Effects of T3SS-positive Pseudomonas isolates on sugar beet growth stimulation and pathogen resistance

Abstract

Background and objective: Understanding the molecular mechanisms underlying plant-microbe interactions harbours great potential for increasing the productivity and resilience of crops. The aim of this study was to investigate the distribution and role of the type III secretion system (T3SS) in non-pathogenic Pseudomonas strains associated with sugar beet (Beta vulgaris L.). The T3SS acts like a molecular syringe that enables bacteria to inject effector proteins directly into host plant cells. While it has been extensively studied in pathogenic bacteria, its role in symbiotic bacteria is still largely unexplored. Methods: The genetic diversity of the isolates was assessed and their T3SS expression was analysed in the presence of sugar beet extract. A T3SS deletion mutant of Pseudomonas marginalis OL141 was generated to study the effects of T3SS on plant growth and pathogen resistance. Results: T3SS was detected in 10 out of 20 Pseudomonas isolates representing seven different species and sharing a conserved region in the hrcT gene. T3SS expression was induced in five isolates by sugar beet extract. P. marginalis OL141 promoted sugar beet growth and increased resistance to Pseudomonas syringae infection, and this effect was abolished by the deletion of T3SS. Conclusion: This study demonstrates the widespread occurrence of T3SS in sugar beet-associated Pseudomonas strains. The results suggest that T3SS-mediated interactions contribute to the promotion of plant growth and resistance to pathogens. Further research is needed to elucidate the detailed mechanisms of T3SS-mediated plant-microbe interactions and their broader implications for agriculture.