Auxin response factor targeted by viruses (PNAS)

Auxin regulates various aspects of plant growth and development and it also contributes to plant defense. Auxin activates downstream signaling by promoting degradation of the repressor Aux/IAA proteins to liberate the key transcription factors ARFs (auxin response factors). Pathogens have been known to mitigate plant defense by targeting Aux/IAA proteins to manipulate plant auxin signaling , but whether ARFs are also targeted by pathogens was unknown. Zhang et al. found that plant viruses target OsARF17, a rice ARF, in multiple ways. They showed that proteins of various types of viruses, including ssRNA viruses, a dsRNA virus, and a negative-sense ssRNA virus interact with different domains of OsARF17, and interfere with its transcriptional or DNA binding activity. Analyses using OsARF17 overexpressing or knock-out plants showed that OsARF17 is a positive regulator of plant defense against these distinct types of plant viruses. This study reveals that OsARF17 plays an important role in defense against various plant viruses, and suggests that distinct viral pathogens have independently evolved strategies to target this key component of auxin signaling to facilitate infection. (Summary by Tatsuya Nobori) Proc. Natl. Acad. Sci. USA 10.1073/pnas.1918254117