| Spermatophyte is the most highly evolved and luxuriant group in plants.They have more developed sporogonium,and reproduced by seeds.Seeds can help plant to spread and conquer unfavorable environmental conditions therefore help spermatophyte to achieve the advantage in the evolutionary history of plant.Germination of the seed is regulated by complicated intrinsic and extrinsic factors,such as light,temperature,phytohormone and architecture and status of the seed per se.Seed dormancy and germination have important significance in agriculture.Seed dormancy benefits the harvest and storage,while timely and uniform seed germination is favorable to growth vigour and production of crops.Seeds that released dormancy can germinate under appropriate condition,while germination will be arrested to protect naive embryos by activating ABA signaling when encountering unfavorable conditions,which is a protective mechanism for seeds under stresses.However,when stress is released or decreased,or staying at a low level,a mechanism counteracting with ABA signaling will allow seeds to germinate,providing a strategy for plants to complete the life cycle and the reproduction.In plant cells,microtubule(MT)organization and alignment play a critical role in regulation of cell division,cell growth and morphogenesis.MT dynamics,organization and array reorientation can not be achieved without the participation of numerous microtubule assosiated proteins(MAPs).The microtubule severing protein katanin is highly conserved in microbe,plant and animal,and is well known to be able to hydrolyze ATP and sever MTs.In Arabidopsis thaliana,researchers had found that katanin p60 subunit(KTN1)participates in leaf epidermis cell,root hair,trichome growth and development,cell wall formation and so on.It also has been reported that KTN1 participates in the post-transcriptional regulation of miRNAs to their target genes,and the miRNA-mediated translational inhibition of their targets requires KTN1 protein.The present research found that although loss of function of KTN1 did not affect seed germination under normal condition,the germination of ktnl mutant seeds was postponed remarkably under osmotic stress,salt stress and in the presence of ABA.In the presence of ABA,it was detected that germination inhibition genes ABI3,ABI4,and ABI5 were highly expressed in ktnl mutant.Previous reports revealed that auxin response genes ARF10/16 play a role in promoting ABI3 expression and subsequently in seed dormancy/germination inhibition,and a microRNA miRNA160 modulates seed dormancy and germination by negatively regulating ARF10/16 expression.Interestingly,ARF10/ARF16 proteins were largely accumulated in ktnl mutant,suggesting a negative regulatory mechanism for ARF 1 0/16 proteins was retarded in ktnl.Further analysis demonstrated that miRNA160 guided ARF10/16 mRNA cleavage was not affected by loss of function of KTN1,but a novel mechanism of miRNA 160 in translational inhibition of ARF10/16 was influenced.Therefore,the negative regulation of ARF10/16 by miRNA160 was partially inhibited in ktnl mutant.Based on those results,we proposed that when seed germinating under stress condition,ABA level and germination inhibition genes expression level are increased in seeds.However,when stress condition is released or reduced,or remained at a low level,a mechanism that down regulation of plant responses to ABA signaling is especially important.The present study revealed that KTN1 mediated miRNA160 translational inhibition of ARF10/16 counteracted with ABA signaling,and inhibited the ABA-induced ABI3 expression.This mechanism will benefit seed germination under low level of stress conditions.The present research revealed a novel translational inhibition mechanism of miRNA160 that regulates its target genes ARF10/16 at a post transcriptional level,and demonstrated a critical role of KTN1 in this process,which provide new insights for further understanding the regulatory mechanisms of seed germination and plant responses to ABA signaling. |
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