Sex-differentiation And Evolution Of Breeding Systems In Androdioecious Tapiscia Sinensis

Tapiscia sinensis Oliv(Tapisciaceae)as one of the tertiary relic plant species,is an endangered species in China famous for its androdioecious breeding system in which populations consist of both of male and hermaphrodite individuals.It has great theoretical value to explore the evolutionary dynamics and evolutionary direction of the angiosperm reproductive system and the evolution of plant life history through the study of the origin and evolution of this androdioecious plant T.sinensis.In this project,T.sinensis was used to compare the patterns of ontogeny and sex differentiation of the bisexual flowers and males.Transcriptome,comparative genomics,and in situ hybridization were uesed to elucidate the mechanism of sex determination.And the focus of this project is to clarify the correlation between the evolution of the reproductive system and sexual dimorphism,and verify the hypothesis that the androdioecy is originated from the ancient bisexual flowers,and reveals the evolution history,motility and direction of the reproductive system of T.sinensis,which adds new evidence to improve the theory of the phylogenetic evolution of angiosperms.The results are as follows: 1.Formation of super-long flower and fruit Development Cycle of T.sinensis(1)In the natural populations,the fruit overwintering strategy of T.sinensis is highly adapted to the current relatively stable alpine environment,which may be the result of long-term adaptation to climate change.(2)It may be the result of convergent evolution that species in different families and genera of independent origin adopt similar breeding strategies.(3)The divergence time of T.sinensis is about 99 Ma,and its super-long reproduction cycle may be formed after the Mid-Miocene.(4)The synchronization of flowers and fruits of T.sinensis results in the reproductive pressure of hermaphroditic individuals.Because the resource allocation is heavily biased towards males,the populations of bisexual individuals are unstable.The emergence of male mutants provides an opportunity for the population continuation of T.sinensis.2.The androdioecious sex system of T.sinensis originated from the ancient hermaphroditic flowersGametogenesis is a key step in the production of ovules or pollen in higher plants.The sex-determination aspects of gametogenesis have been well characterized in the model plant Arabidopsis.However,little is known about this process in androdioecious plants.T.sinensis Oliv.is a functionally androdioecious tree,with both male and hermaphroditic individuals.Hermaphroditic flowers(HFs)are female-fertile flowers that can produce functional pollen and set fruits.However,compared with male flowers(MFs),the pollen viability and number of pollen grains per flower are markedly reduced in HFs.MFs are female-sterile flowers that fail to set fruit and that eventually drop.Compared with HF,a notable cause of MF female sterility in T.sinensis is when the early gynoecium meristem is disrupted.During the early stage of HF development(stage 6),the ring meristem begins to form as a ridge around the center of the flower.At this stage,the internal fourth-whorl organ is finger-like rather than carpelloid in MF.Evidences from floral development and phylogeny imply that(1)T.sinensis belongs to Type I unisexual flower development model;(2)androdioecy as an intermediate sexual system might evolve from ancestral hermaphroditism in T.sinensis.The first step is a female-sterility mutation(vestigial ovary present),giving rise to an androdioecious state;the second step is that bisexual flowers tend to evolve into females through vestigial male function(pollen abortion/lower pollen viability).In conclusion,T.sinensis shows different degrees of reduction between male flowers and bisexual ones in the evolution to dioecy.3.Various regulatory pathways involved in sex differentiation of T.sinensisThe transcriptome data analysis showed that:(1)ethylene may be the upstream factor of gynoecium development in T.sinensis,and auxin and cytokinin signal transduction are the basis of gynoecium primordia formation.Ethylene treatment with 50 mg/L of ethephon could promote the sex change of male flowers,which indicated that ethylene participated in the sex differentiation of T.sinensis.(2)C-class Mads-box genes is involved in the determination of the fourth round of flower organs.In situ hybridization results show that Ts AG is related to the formation of gynoecium primordia and is involved in the development of stamens.(3)The pollen viability of amphoteric flowers of T.sinensis is low and some pollen abortion occurs.Auxin signaling pathway is considered to be related to pollen abortion and is essential for female gametophyte development.In this paper,pathways for the female-sterility model were initially proposed to shed light on the molecular mechanisms of gynoecium development at early stages in T.sinensis.