Tomato Stress-Associated Protein 4 Contributes Positively to Immunity against Necrotrophic Fungus Botrytis cinerea.

Stress-associated proteins (SAPs) are A20/AN1 domain-containing proteins, some of which play important roles in plant stress signaling. Here, we report the involvement of tomato SlSAP family in immunity. SlSAPs responded with different expression patterns to Botrytis cinerea and defense signaling hormones. Virus-induced gene silencing of each of SlSAPs and disease assays revealed that SlSAP4 and SlSAP10 play roles in immunity against B. cinerea. Silencing of SlSAP4 resulted in attenuated immunity to B. cinerea, accompanying with increased accumulation of reactive oxygen species and downregulated expression of JA/ET signaling responsive defense genes. Transient expression of SlSAP4 in Nicotiana benthamiana led to enhanced resistance to B. cinerea. Exogenous application of MeJA partially restored the resistance of the SlSAP4-silenced plants against B. cinerea. SlSAP4 interacted with three of four SlRAD23 proteins. The A20 domain in SlSAP4 and the UBA domains in SlRAD23d are critical for SlSAP4-SlRAD23d interaction. Silencing of SlRAD23d led to decreased resistance to B. cinerea but silencing of each of other SlRAD23s did not affect immunity against B. cinerea. Furthermore, silencing of SlSAP4 and each of SlRAD23s did not affect immunity to Pseudomonas syringae pv. tomato DC3000. These data suggest that SlSAP4 contributes positively to tomato immunity against B. cinereal through affecting JA/ET signaling and may be involved in the substrate ubiquitination process via interacting with SlRAD23d.