The Molecular Mechanism Of AP2-like Transcription Factor TOE1 Involved In Ethylene Response By Regulating EIN3 Transcription

Age pathway regulates every step of plant transition from seed germination,vegetative growth to reproductive growth.Plant development regulated by age is mainly dependent on the role of micro RNAs.For example,mi R156 suppresses cell death to delay plant senescence,while mi R172 promotes the transition from juvenile to adult phase.mi R172 participates in regulating flowering and plant innate immunity through directly inhibiting the expression of genes encoding APETALA 2(AP2)like transcription factors.TARGET OF EAT1(TOE1)and TOE2 both belong to APETALA2(AP2)like transcription factors.TOE1 promotes plant flowering through directly inhibiting FLOWERING LOCUS T(FT)expression.Ethylene is one of the most important plant hormones that promote plant senescence.ETHYLENE INSENSITIVE 3(EIN3)and EIN3 LIKE 1(EIL1)transcription factors are key factors in activating ethylene responses.As plants age,EIN3 protein gradually accumulated.A recent research showed that EIN3 inhibited de novo root regeneration through suppressing downstream gene WUSCHEL RELATED HOMEOBOX(WOX)expression.However,the mechanism of age upregulating EIN3 expression is unknown,and it is not clear whether the age pathway and ethylene signaling interact with each other during other plant development.This study firstly found that AP2 like transcription factor TOE1 could bind to the promoter of EIN3.EIN3 genes expression and EIN3 protein accumulation in toe1 toe2 mutants was significantly higher than in the wild type,demonstrating TOE1 could directly suppress EIN3 expression.The etiolated seedlings of toe1 toe2 mutants in darkness had stronger ethylene triple response than the wild type,which suggested TOE1 inhibited triple response.The capacity of root regeneration of toe1 toe2 mutants is significantly lower than wild type.However,the mutant of ein3 eil1 is able to restore the low capacity of regeneration in toe1 toe2 mutants,indicating that TOE1 promote root regeneration through inhibiting EIN3 transcription.Plant hormone auxin plays a vital role in regulating root regenerative capacity.ANTHRANILATE SYNTHASE ?1(ASA1)encodes a key synthase responsible for auxin biosynthesis.After plant injured,ASA1 is immediately upregulated to promote auxin accumulation.Ch IP-seq results in previous research implied ASA1 may be a target gene of EIN3.This study proved that EIN3 could bind to the promoter of ASA1 through EMSA,and ethylene biosynthesis precursor ACC inhibited ASA1 expression.These results suggested that EIN3 could inhibit ASA1 expression by directly binding to ASA1 promoter to suppress regeneration.Although ethylene inhibits seedings to elongate root in light,the root length of toe1toe2 mutant is longer than wild type.This result suggested that TOE1 maybe regulates root development through other mechanism.And ethylene and age both could accelerate plant leaf senescence,the phenotype of leaf senescence of toe1 toe2 mutant was similar to wild type.It is indicated that TOE1 fail to regulate leaf senescence.In conclusion,we found that AP2 like transcription factor TOE1 is involved in a part of ethylene response by regulating the transcription of EIN3.And EIN3 maybe inhibit root regeneration through directly suppressing ASA1 expression.Above results indicated that the age pathway and ethylene signaling pathway are interrelated through the TOE1-EIN3 regulatory module.