The ubiquitin ligase SEVEN IN ABSENTIA ( SINA ) ubiquitinates a defense‐related NAC transcription factor and is involved in defense signaling

Summary We recently identified a defense‐related tomato ( Solanum lycopersicum ) NAC ( NAM , ATAF 1,2, CUC 2) transcription factor, NAC 1, that is subjected to ubiquitin–proteasome system‐dependent degradation in plant cells. In this study, we identified a tomato ubiquitin ligase (termed SEVEN IN ABSENTIA 3; SINA 3) that ubiquitinates NAC 1, promoting its degradation. We conducted coimmunoprecipitation and bimolecular fluorescence complementation to determine that SINA 3 specifically interacts with the NAC 1 transcription factor in the nucleus. Moreover, we found that SINA 3 ubiquitinates NAC 1 in vitro and promotes NAC 1 degradation via polyubiquitination in vivo , indicating that SINA 3 is a ubiquitin ligase that ubiquitinates NAC 1, promoting its degradation. Our real‐time PCR analysis indicated that, in contrast to our previous finding that NAC 1 mRNA abundance increases upon Pseudomonas infection, the SINA 3 mRNA abundance decreases in response to Pseudomonas infection. Moreover, using Agrobacterium ‐mediated transient expression, we found that overexpression of SINA 3 interferes with the hypersensitive response cell death triggered by multiple plant resistance proteins. These results suggest that SINA 3 ubiquitinates a defense‐related NAC transcription factor for degradation and plays a negative role in defense signaling.