The Ethylene Biosynthesis Genes ACS2 and ACS6 Modulate Disease Severity of Verticillium dahliae

Verticillium dahliaeis one of the most destructive soilborne plant pathogens since it has a broad host range and there is no chemical disease management. Therefore, there is a need to unravel the molecular interaction between the pathogen and the host plant. For this purpose, we examined the role of 1-aminocyclopropane-1-carboxylic acid synthases (ACSs) ofArabidopsis thalianauponV. dahliaeinfection. We observed that theacs2,acs6, andacs2/6plants are partially resistant toV. dahliae, since the disease severity of theacsmutants was lower than the wild type (wt) Col-0 plants. Quantitative polymerase chain reaction analysis revealed thatacs2,acs6, andacs2/6plants had lower endophytic levels ofV. dahliaethan the wt. Therefore, the observed reduction of the disease severity in theacsmutants is rather associated with resistance than tolerance. It was also shown thatACS2andACS6were upregulated uponV. dahliaeinfection in the root and the above ground tissues of the wt plants. Furthermore, the addition of 1-aminocyclopropane-1-carboxylic acid (ACC) and aminooxyacetic acid (AOA), the competitive inhibitor of ACS, in wtA. thaliana, before or afterV. dahliaeinoculation, revealed that both substances decreasedVerticilliumwilt symptoms compared to controls irrespectively of the application time. Therefore, our results suggest that the mechanism underpinning the partial resistance ofacs2andacs6seem to be ethylene depended rather than ACC related, since the application of ACC in the wt led to decreased disease severity compared to control.