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.