In-depth evaluation of root infection systems with the vascular fungus Verticillium longisporum as soil-borne model pathogen

PREMISEWhile leaves are far more accessible for analysing plant defences, roots are hidden in the soil leading to difficulties in studying soil-borne interactions. Literature describes inoculation strategies to infect model plants with model root pathogens, but it remains demanding to obtain a methodological overview. To address this challenge, this study uses the model root pathogen Verticillium longisporum on Arabidopsis thaliana and provides recommendations based on evident examples for the selection and management of suitable infection systems to investigate root-microbe interactions. METHODS AND RESULTSA novel root infection system is introduced, while two existing ones are precisely described and optimized. Advantages and disadvantages of each are assessed, step-by-step protocols are presented and accompanied by pathogenicity tests, transcriptional analyses of indole-glucosinolate markers and independent confirmations using reporter constructs. The results validate the importance of indole-glucosinolates as secondary metabolites limiting V. longisporum propagation in hosts. DISCUSSIONWe provide detailed guidelines for studying host responses and defence strategies against V. longisporum. Furthermore, other soil-borne microorganisms or other model plants, such as economically important oilseed rape, can be used in the infection systems described. Hence, these proven manuals help to find a root infection system for your specific research questions to decipher root-microbe interactions.