Increased resistance to <i>Verticillium dahliae</i> in <i>Arabidopsis</i> plants defective in auxin signalling

Abstract

Auxin signalling and transport participate in plant–microbe interactions as positive or negative regulators of disease resistance. The present study investigated the responses of Arabidopsis thaliana plants impaired in the auxin receptors TIR 1, AFB 1 and AFB 3 and the auxin transporter AXR 4, upon infection by the soilborne root pathogen Verticillium dahliae . Fewer symptoms were recorded in afb1 , afb3 and axr4 plants compared to the wild type (wt). qPCR analysis revealed that the decrease in symptom severity in afb1 , afb3 and axr4 was correlated with reduction in the growth of the pathogen in the plants. Therefore, afb1 , afb3 and axr4 are partially resistant to V. dahliae . Upon V. dahliae infection, the expression of TIR 1 , AFB 1 , AFB 3 and AXR 4 was up‐regulated in roots, while indole‐3‐acetic acid levels were similar to mocks. The partial resistance of afb1 , afb3 and axr4 against V. dahliae can be attributed in part to the up‐regulation of defence‐related genes, as it was observed that afb1 and axr4 had higher PR 1 levels than wt, while afb3 had higher PDF 1.2 levels than wt. The findings of the present study suggest that the auxin signalling defective mutants afb1 , afb3 and axr4 show increased resistance against V. dahliae .