Suppressing an AUX/IAA gene GhIAA43 expression activates the SA-mediated immune pathway and enhances Verticillium wilt resistance in cotton

Salicylic acid (SA) and auxin often exert antagonistic effects during pathogen challenge, and SA’s inhibitory effect on auxin-mediated signaling pathway plays a crucial role in plant defense mechanisms. However, whether SA-mediated immunity can be enhanced through the inhibition of auxin signaling pathway remains unclear. Cotton GhIAA43, a member from the Aux/IAA family, was a resistance-related gene against Verticillium dahliae attack. Here, we clarified the role of GhIAA43 in regulating the auxin and SA-mediated pathways to improve the plant resistance by using the RNA interference (RNAi)-GhIAA43 cotton plants and GhIAA43-overexpressing Arabidopsis lines. Both RNAi-GhIAA43 cotton and GhIAA43-overexpressing Arabidopsis exhibited the enhanced plant resistance to V. dahliae. In GhIAA43-overexpressing Arabidopsis, more auxin pathways were activated, resulting in the increased lignin content and robust root development, which enhances the plant physical resistance. Whereas in RNAi-GhIAA43 cotton, the auxin signal transduction pathway was inhibited, leading to the reduction of lignin content, the decrease of H₂O₂ scavenging ability, while the increase of H₂O₂ levels and activation of the SA immune pathway, which confers the plant resistance. This study indicates that SA-mediated immune pathway can be activated by modulating auxin signaling component Aux/IAA protein, also provides a strategy for improving Verticillium wilt resistance by the knockdown of GhIAA43 in cotton breeding practice.