An oomycete effector that induces shade avoidance-like growth and suppresses plant defences targets the AUX/IAA protein IAA11

Filamentous pathogens, such as oomycetes, employ multiple strategies to suppress plant immunity, including manipulation of phytohormone signalling pathways. The effector HaRxL106 from the oomycete Hyaloperonospora arabidopsidis (Hpa), whose expression in planta induces shade avoidance syndrome (SAS)-like growth, has previously been shown to interact with BIM1, a transcription factor involved in brassinosteroid signalling. Here, we present evidence that HaRxL106 interacts with another key host target, the AUX/IAA protein IAA11, a negative regulator of auxin responses. Our data suggest that HaRxL106 may impede the repressive function of IAA11, affecting auxin signalling, which in coordination with an enhanced brassinosteroid output suppresses plant immune responses. These findings provide insights into how pathogen effectors manipulate plant growth and immunity to facilitate infection.