Unisexual Pistillate Flower Regeneration in Immature Embryo Culture of Wheat

In this experiment, floral development from tissue culture of bread wheat (Triticum aestivum L.) was investigated. Immature embryos of 45 wheat cultivars were cultured, and 11.1% of the genotypes regenerated floral organs from the calli near the bases of the green buds or plantlets regenerated. The floral buds were morphologically incomplete with the appearances of unisexual pistillate flowers which were naked, clustered with normal ovaries and exuberant feather-like stigmas, but without stamens, paleas, lemmas and glumes. The histological examination showed that the pistils originated from the meristematic cells near the green buds or plantlets, and the clustered pistils were formed by secondary pistillate regeneration. The development of the feather-like structures was earlier than that of the ovules. Biovule developed from an ovary besides normal uniovule. Statistical analysis by X 2 test for independency demonstrated highly significant difference of flower regeneration among the tested genotypes. Wheat cultivar YA-1 revealed higher percentage (44.4%) than other genotypes, and the response could well be repeated in different years. It was indicated that the floral regeneration of immature embryo explants of YA-1 is relatively stable. The frequency of floral regeneration was mainly regulated by the components in the subculture media, compared with the response of the dedifferentiation media, despite the obviously different components involving basal medium type, inorganic Fe2+ concentration and plant growth regulators. The results suggested the combination of 6-benzylaminopurine, alpha-naphthalene acetic-acid and doubled inorganic Fe2+ might be more beneficial to inducing the floral development than that of 2,4-D and normal inorganic Fe2+ concentration in subculture medium. However, both immature inflorescence and mature embryo, as cultured explants of YA-1, did not regenerate any flower organs. It is believed that the immature embryo culture of YA-1 can be used to establish ideal experimental system for the study of floral developmental mechanism in wheat.

Evolutionary mechanisms and practical significance of reproductive success and clonal diversity in unisexual vertebrate polyploids

Unisexual reproduction is generally relevant to polyploidy, and unisexual vertebrates are often considered an evolutionary “dead end” due to the accumulation of deleterious mutations and absence of genetic diversity. However, some unisexual polyploids have developed strategies to avoid genomic decay, and thus provide ideal models to unveil unexplored evolutionary mechanisms, from the reproductive success to clonal diversity creation. This article reviews the evolutionary mechanisms for overcoming meiotic barrier and generating genetic diversity in unisexual vertebrates, and summarizes recent research advancements in the polyploid Carassius complex. Gynogenetic gibel carp(Carassius gibelio) is a unique amphitriploid that has undergone a recurrent autotriploidy and has overcome the bottleneck of triploid sterility via gynogenesis. Recently, an efficient strategy in which ploidy changes, including from amphitriploid to amphitetraploid, then from amphitetraploid to novel amphitriploid, drive unisexual-sexual-unisexual reproduction transition and clonal diversity has been revealed.Based on this new discovery, multigenomic reconstruction biotechnology has been used to breed a novel strain with superior growth and stronger disease resistance. Moreover, a unique reproduction mode that combines both abilities of ameiotic oogenesis and sperm-egg fusion,termed as ameio-fusiongensis, has been discovered, and it provides an efficient approach to synthesize sterile allopolyploids. In order to avoid ecological risks upon escape and protect the sustainable property rights of the aquaculture seed industry, a controllable fertility biotechnology approach for precise breeding is being developed by integrating sterile allopolyploid synthesis and gene-editing techniques.This review provides novel insights into the origin and evolution of unisexual vertebrates and into the attempts being made to exploit new breeding biotechnologies in aquaculture.

Evolution of parthenogenetic reproduction in Caucasian rock lizards:A review

Despite numerous works devoted to hybrid origin of parthenogenesis in reptiles,the causes of hybridization between different species,resulting in the origin of parthenogenetic forms,remain uncertain.Recent studies demonstrate that sexual species considered parental to parthenogenetic rock lizards(Darevskia spp.)avoid interspecific mating in the secondary overlap areas.A specific combination of environmental factors during last glaciation period was critical for ectotherms,which led to a change in their distribution and sex ratio.Biased population structure(e.g.,male bias)and limited available distributional range favored the deviation of reproductive behavior when species switched to interspecific mates.To date,at least 7 diploid parthenogenetic species of rock lizards(Darevskia,Lacertidae)originated through interspecific hybridization in the past.The cytogenetic specifics of meiosis,in particular the weak checkpoints of prophase l,may have allowed the formation of hybrid karyotypes in rock lizards.Hybridization and polyploidization are 2 important evolutionary forces in the genus Darevskia.At present,throughout backcrossing between parthenogenetic and parental species,the triploid and tetraploid hybrid individuals appear annually,but no triploid species found among Darevskia spp.on current stage of evolution.The speciation by hybridization with the long-term stage of diploid parthenogenetic species,non-distorted meiosis,together with the high ecological plasticity of Caucasian rock lizards provide us with a new model for considering the pathways and persistence of the evolution of parthenogenesis in vertebrates.

Regain of sex determination system and sexual reproduction ability in a synthetic octoploid male fish

Polyploids in vertebrates are generally associated with unisexual reproduction,but the direct consequences of polyploidy on sex determination system and reproduction mode remain unknown.Here,we synthesized a group of artificial octoploids between unisexual gynogenetic hexaploid Carassius gibelio and sexual tetraploid Carassius auratus.The synthetic octoploids were revealed to have more than 200 chromosomes,in which 50 chromosomes including the X/Y sex determination system were identified to transfer from sexual tetraploid C.auratus into the unisexual gynogenetic hexaploid C.gibelio.Significantly,a few synthetic octoploid males were found to be fertile,and one octoploid male was confirmed to regain sexual reproduction ability,which exhibits characteristics that are the same to sexual reproduction tetraploid males,such as 1:1 sex ratio occurrence,meiosis completion and euploid sperm formation in spermatogenesis,as well as normal embryo development and gene expression pattern during embryogenesis.Therefore,the current finding provides a unique case to explore the effect of sex determination system incorporation on reproduction mode transition from unisexual gynogenesis to sexual reproduction along with genome synthesis of recurrent polyploidy in vertebrates.

Obligatory parthenogenesis and TE load： Bacillus stick insects and the R2 non-LTR retrotransposon

Transposable elements （TEs） are selfish genetic elements whose self-replication is contrasted by the host genome. In this context, host reproductive strategies are predicted to impact on both TEs load and activity. The presence and insertion distribution of the non- LTR retrotransposon R2 was here studied in populations of the strictly bisexual Bacillus grandii maretimi and of the obligatory parthenogenetic Bacillus atticus atticus. Further- more, data were also obtained from the offspring of selected B. a. atticus females. At the population level, the gonochoric B. g. maretimi showed a significantly higher R2 load than the obligatory parthenogenetic B. a. atticus. The comparison with bisexual and unisexual Bacillus rossius populations showed that their values were higher than those recorded for B. a. atticus and similar, or even higher, than those of B. g. maretimi. Consistently, an R2 load reduction is scored in B. a. atticus offspring even if with a great variance. On the whole, data here produced indicate that in the obligatory unisexual B. a. atticus R2 is active and that mechanisms of molecular turnover are effective. Furthermore, progeny analyses show that, at variance of the facultative parthenogenetic B. rossius, the R2 activ- ity is held at a lower rate. Modeling parental-offspring inheritance, suggests that in B. a. atticus recombination plays a major role in eliminating insertions rather than selection, as previously suggested for unisexual B. rossius progeny, even if in both cases a high variance is observed. In addition to this, mechanisms of R2 silencing or chances of clonal selection cannot be ruled out.