Role Of Repressor Proteins OsJAZs In Modulating Sensitivity Of Jasmonate Signaling

Jasmonates(JAs)are oxylipin phytohormones that critically coordinate plant stress responses and development.In Arabidopsis thaliana,JA signaling depends on JASMONATE-ZIM DOMAIN(JAZ)proteins.Genetic,molecular and crystallographic analysis showed that the JAZ co-receptor COI1 binds active JA or the JA-mimicking phytotoxin,coronatine(COR),the N-terminal(degron)of the Jas domain of JAZ protein changed from a helix to a ring structure,which are destroyed by the SCF^COI1-mediated 26S proteasome.JAZ degradation releases JAZ-interacting transcription factors that can execute stress and growth responses.Jas motifs undergo conformational changes during JA signal transduction and are important for the JAZ-COI1 interaction and JAZ protein degradation.Our previous studies have shown that jasmonate synthesis,metabolism and signal transduction pathways in rice are similar to Arabidopsis thaliana.Os JAZ1 is a major suppressor protein in jasmonate signaling pathway.Os COI1b and Os MYC2 can interact with receptor proteins,and activating the transformation from spikelets to floral organs by regulating the timely expression of E-type MADS proteins such as Os MADS1.However,how alterations in the Jas motif,and in particular the JAZ degron,influence protein stability and plant development have not been well explored.In order to further study this biological problem,molecular and genetic experiments such as yeast two-hybrid(Y2H),CRISPR-Cas9-mediated gene directed knockout and overexpression experiments were used to analyze the molecular mechanism of Os JAZ1 protein degron sequence polymorphism in regulating jasminate signal in rice.The main conclusions are as follows:1.Rice JAZ protein has conserved and semi-conserved Jas domain and degron sequence.Y2H experiment showed that degron sequence mediated the interaction between Os JAZ1 and Os COI1b.The replacement or deletion of core amino acids in degron fragment could change the COR-dependent interaction between Os JAZ1-Os COI1b.COR concentration gradient analysis showed that the polymorphism of Os JAZ1 degron sequence affected the sensitivity of Os JAZ1-Os COI1b interaction.2.Substitution or deletion of degron sequence of Os JAZ1 protein may hinder jasmonate signal transduction and affect the normal development of rice flowers.It was found that degron sequence regulated root growth under different concentrations of Me JA.These results confirmed that degron sequence not only regulates the stability and specificity of jasmonate signal transduction,but also acts as a sensitivity regulator of JA signal transduction.3.COR treatment with different concentrations showed that the interaction between Os JAZ6-Os COI1b was more sensitive than that between Os JAZ1-Os COI1b.Os JAZ1,Os JAZ2 and Os JAZ8 overexpression in 9522 have no defects in spikelet development,but overexpression of Os JAZ6 in 9522 and dominant mutant of Os JAZ1(eg2-1D)significantly inhibited JA signal transduction.These results showed that Os JAZ6 may be more sensitive repressing JA signallling.4.Biochemical and genetic experiments showed that Os JAZ6 is also a repressor in jasmonate signal transduction,which might interact with Os JAZ1 to balance JA signal transduction.Therefore,these studies provide a foundation for further study of the molecular mechanism of Os JAZ protein complexes in buffering JA signal transduction.