Rose WRKY13 promotes disease protection to Botrytis by enhancing cytokinin content and reducing abscisic acid signaling

The plant hormones cytokinin (CK) and abscisic acid (ABA) play critical and often opposite roles during plant growth, development, and responses to abiotic and biotic stresses. Rose (Rosa sp.) is an economically important ornamental crop sold as cut flowers. Rose petals are extremely susceptible to gray mold disease caused by the necrotrophic fungal pathogen Botrytis cinerea. The infection of rose petals by B. cinerea leads to tissue collapse and rot, causing severe economic losses. In this study, we showed that CK and ABA play opposite roles in the susceptibility of rose to B. cinerea. Treatment with CK enhanced the disease protection of rose petals to B. cinerea, while ABA promoted disease progression. We further demonstrated that rose flowers activate CK-mediated disease protection via a B. cinerea-induced rose transcriptional repressor, Rosa hybrida (Rh)WRKY13, which is an ortholog of Arabidopsis (Arabidopsis thaliana), AtWRKY40. RhWRKY13 binds to promoter regions of the CK degradation gene CKX3 (RhCKX3) and the ABA-response gene ABA insensitive4 (RhABI4), leading to simultaneous inhibition of their expression in rose petals. The increased CK content and reduced ABA responses result in enhanced protection from B. cinerea. Collectively, these data reveal opposite roles for CK and ABA in the susceptibility of rose petals against B. cinerea infection, which is mediated by B. cinerea-induced RhWRKY13 expression.