Arabidopsis F-box protein prolongs JA-based defense response. Commentary in Molecular Plant.
As highly respected jasmonate experts, Claus Wasternack and Bettina Hause recently had the honor of commenting on an article by Zhang et al. in the renowned journal Molecular Plant. The subject of the reviewed study is the Botrytis cinerea-induced F-box protein 1 (BFP1) in Arabidopsis, which is expressed upon infection with the gray mold pathogen and increases the plant's resistance to the pathogen by inhibiting jasmonic acid degradation.
In general, the jasmonate (JA) signaling pathway in Arabidopsis is based on the following scenario: In the unstressed state of the plant, the JA concentration is low and all JA-responsive genes are blocked in their activity by repressors, the JAZ proteins. An infection with Botrytis cinerea or other pathogens leads to a massive increase of the phytohormone within the infected cells. JA, now present in excess, binds to the COI1 receptor, which is the dominant F-box protein in the JA-mediated defense response. The binding of the phytohormone causes a coupling of JAZs to COI1, resulting in ubiquitin-mediated degradation of JAZ repressors. Thus, JAZs no longer repress JA-inducible promoters, and with the help of transcription factors such as MYC2, the expression of downstream genes for the production of defense compounds against the pathogen can take place.
However, in addition to COI1, Arabidopsis contains 700 F-box proteins and the question arose whether other F-box proteins play a role in the JA signaling pathway. In their study, Zhang et al. did indeed find the Arabidopsis F-box protein BFP1, which is specifically involved in resistance to B. cinerea. According to their results, BFP1 acts by binding to JA oxidases and directing them towards ubiquitination and thus degradation. JA oxidases catalyze the oxidation of JA to the inactive 12-OH-JA and therefore are important in the termination of JA signaling. Consequently, BFP1 helps to uphold the immune response as it inhibits the degradation of the active JA molecules. Zhang et al. showed for the first time that plant immunity is not only achieved through the direct effect of phytohormones, but can also be increased by preventing the degradation of phytohormones and thus effectively extending their period of action. In their study, Zhang et al. clearly demonstrated that also the degradation of JA derivatives plays an important role in the plant immune response. In this scenario, BPF1 acts exclusively as a positive regulator of JA-dependent defense processes and does not cause any further energetic costs at the expense of fitness. This could be harnessed in the future for the development of more resistant plant varieties, the authors conclude.