Identification Of Regulatory Mechanism In Achene And Receptacle During Fruit Initiation And Ripening Transition In Fragaria Vesca

Formation of fruit is an evolutionary success of angiosperms.Function of fruit is considered to protect and nourish the developmental seeds,and facilitate efficient seed dispersal at maturity.Most studies on the regulatory mechanism of fruit development focus on the whole fruit.The mutual regulation between seed and fruit is not well understood during fruit development.Strawberry fruit consists of receptacle(fruit)and achene(seed)attaching on the receptacle,which is a good model for investigating the relationship between seed and fruit during fruit development and ripening.In strawberry,auxin which is produced by the fertilized achenes is important for promoting receptacle expansion.However,the regulatory mechanism for fruit set and the relationship between achene and receptacle are largely unknown.Here,we find that pollination can promote the fruit development(both achene and receptacle),and the fruit enlargement can also be induced by exogenous auxin treatment.Interestingly,auxin is highly accumulated in achene but not in receptacle after pollination and fertilization.Further transcriptome analysis shows that only a small portion of the differentially expressed genes are induced by pollination and exogenous auxin treatment.Auxin,but not pollination,is able to activate the expression of growth-related genes especially in receptacle,which resulted in its fast growth.Meanwhile,those genes which are involved in some other hormone pathways such as GA and cytokinin are also regulated by exogenous auxin treatment but not pollination.This suggest that pollination is not able to activate auxin responses in receptacles but produce auxin in the fertilized achenes.The produced auxin may transport or transduce from achene to receptacle and promote the fast fruit growth at the early stage of fruit initiation.Our work reveals a potential coordination between achene and receptacle during fruit set,and auxin may be a key coordinator.Signal interaction between achene and receptacle not only acts important role during fruit set,but also regulates the development and ripening processes after fruit growth initiation.In this study,we investigate the molecular mechanism for signal interaction between achene and receptacle during fruit ripening transition.Here,the transcriptome analysis is performed to investigate gene expression variation during strawberry fruit ripening transition.From S6 to RS1,a large number of differentially expressed genes(DEGs)are screened out in both achene and receptacle,and there are significant differences between achene and receptacle.Among the DEGs,FvCKX1,which is differentially expressed in both achenes and receptacles,is identified.Moreover,FvCKX1 shows opposite expression trends between achene and receptacle.Transient silencing of FvCKX1 significantly promotes receptacle enlargement but inhibits achene maturation.Overexpression of FvCKX1 inhibits receptacle enlargement while promotes achene maturation.Moreover,ABA content is higher accumulated in the receptacle of FvCKX1-RNAi,and significantly decreased in the FvCKX1-OE receptacle.ABA is reported to positively regulate fruit enlargement.The results suggest that FvCKX1 is involved in the regulation of strawberry fruit ripening transition,and possibly though the regulation of ABA content.Altogether,this study firstly characterizes the achene and receptacle growth profile,and outlines the transcriptome variation between achene and receptacle in responding fruit growth initiation and ripening transition in detail.Our study also verifies the important role of phytohormones during phase change,and selects out the genes participating in achene and receptacle development.After all,our work provides a new theoretical basis for the regulation of strawberry fruit development.