Identification of a strawberry NPR-like gene involved in negative regulation of the salicylic acid-mediated defense pathway

Hormonal modulation plays a central role in triggering various resistant responses to biotic and abiotic stresses in plants. In cultivated strawberry (Fragaria x ananassa), the salicylic acid (SA)-dependent defense pathway has been associated with resistance to Colletotrichum spp. and the other pathogens. To better understand the SA-mediated defense mechanisms in strawberry, we analyzed two strawberry cultivars treated with SA for their resistance to anthracnose and gene expression profiles at 6, 12, 24, and 48 hr post-treatment. Strawberry genes related to SA biosynthesis, perception, and signaling were identified from SA-responsive transcriptomes of the two cultivars, and the induction of 17 candidate genes upon SA treatment was confirmed by qRT-PCR. Given the pivotal role of the non-expressor of pathogenesis-related (NPR) family in controlling the SA-mediated defense signaling pathway, we then analyzed NPR orthologous genes in strawberry. From the expression profile, FaNPRL-1 [ortholog of FvNPRL-1 (gene20070 in F. vesca)] was identified as an NPR-like gene significantly induced after SA treatment in both cultivars. With a conserved BTB/POZ domain, ankyrin repeat domain, and nuclear localization signal, FvNPRL-1 was found phylogenetically closer to NPR3/NPR4 than NPR1 in Arabidopsis. Ectopic expression of FvNPRL-1 in the Arabidopsis thaliana wild type suppressed the SA-mediated PR1 expression and the resistance to Pseudomonas syringae pv. tomato DC3000. Transient expression of FvNPRL-1 fused with green fluorescent protein in Arabidopsis protoplasts showed that SA affected nuclear translocation of FvNPRL-1. FvNPRL-1 likely functions similar to Arabidopsis NPR3/NPR4 as a negative regulator of the SA-mediated defense.