Viral action on the auxin signaling repressor IAA16 reveals a conserved negative regulator of plant growth and immunity

Crop breeding endeavors are frequently constrained by the growth-defense trade-off, and uncoupling this trade-off remains challenging due to the limited knowledge of master regulators. Geminivirus-betasatellite complexes, through the betasatellite-encoded protein βC1, suppress auxin-mediated plant growth and salicylic acid (SA)-mediated immunity. βC1 interacts with and prevents the degradation of plant IAA16 by blocking ATL52-mediated ubiquitination. IAA16 functions as a negative regulator of both auxin and SA signaling pathways. IAA16 interacts with OBP4 to promote the transcription of the SA-signaling repressor NPR3. Notably, regulation of auxin and SA signaling by IAA16, as well as viral manipulation of IAA16 stability, appears to be conserved, as they were documented in tomato plants. Together, our study of viral action on IAA16 reveals a negative regulator of both plant growth and immunity. These findings open fresh avenues for understanding viral manipulation of plant growth and immunity and suggest potential targets for crop improvement.