Study On The Molecular Mechanism Of Ethylene Regulating De Novo Regeneration Of Arabidopsis Roots

Detached plant organs have a powerful ability to regenerate new organs from parts of the remaining tissues and then form an intact plant.For example,adventitious roots can regenerate from the cutting site in Arabidopsis leaf explants without any exogenous plant hormone treatments.This process is known as de novo root regeneration(DNRR).However,the precise regulatory mechanisms underlying DNRR are not completely understood.Just as the tissue repair ability declines in older human beings,so does the regeneration capacity of plants decline with age.Detached Arabidopsis thaliana leaf explants can regenerate adventitious roots at the cutting site without the need for exogenous hormones,but this regeneration ability decreases with age.Ethylene has long been considered as a plant senescence hormone,which can coordinate plant internal and external signals to promote leaf senescence.In this study,we used a simple assay to dissect why older plants exhibit lower regeneration rates and whether it is related to the plant hormone ethylene.Here,we show that ethylene treatment or genetic activation of ETHYLENE INSENSITIVE 3(EIN3)strongly suppresses DNRR rates,while a mutant lacking EIN3 and its homolog EIL1(ein3 eil1)displays a higher DNRR capacity.Previous reports have shown that the sequential induction of WUSCHEL RELATED HOMEOBOX 11(WOX11)/WOX12 and WOX5/WOX7 expression is required for the establishment of DNRR.We found that EIN3 directly targets WOX11 and WOX5 promoter regions to suppress their transcription.Furthermore,older plants show enhanced EIN3 transcription and activity,and repressed expression of WOX11 and WOX5.While rooting rates strongly decline in 22-day-old wild-type plants,the ein3 eil1 double mutant still exhibits strong DNRR in 30-day-old plants.Together,these results illustrate that plant aging takes advantage of EIN3 as a negative regulator to suppress DNRR at least through inhibiting the activation of WOX genes.