Research progress of sex determination and sex-linked markers in persimmon

Abstract：Persimmon (Diospyros kaki Thunb.) is originated and domesticated in China. Artificial control of sexuality is an important issue for both fruit production and breeding of leading persimmon cultivars. Complex sexualities occurred in Diospyros L., and individual persimmon floral phenotypes can be generally divided into four types: gynoecious (bearing female flowers only, most cultivars) , androecious (bearing male flowers only, few cultivars) , monoecious (bearing both male and female flowers, few cultivars) and trimonoecious (bearing both bisexual and unisexual flowers, rare cultivars) . Some gynoecious genotypes, such as Japanese PCNA (pollination constant non-astringent) cultivars‘Fuyuu'and‘Jirou', can occasionally generate male flowers under certain circumstance. The goal of this article is to review the nature of sexual dimorphism in Diospyros L. and discuss the androecious genotypes benefits in persimmon orchard production. The genetic control of sex determination is gradually understood in Diospyros L.. Sex expression was influenced by many factors including hormone, tree age, nutrient status and environment, etc.. Low concentration of indoleacetic acid (IAA) , abscisic acid (ABA) , the ratio of ABA to IAA, and high levels of gibberellin A3 (GA3) in male floral buds in the middle of June were correlated to the formation of three-flower cymes. In addition, high levels of the ratio of ABA to zeatin (ZT) might promote the differentiation of male floral buds. Benzylaminoadenine (BA) treatment leads staminate flowers to hermaphroditic flowers. The balance between cytokinins, auxins and abscisic acid plays a vital role in persimmon sex expression. Persimmon pistillate and staminate floral primordia inthe buds of current shoots initiated to differentiate in early June, then quiescent and overwintered. The floral structure restarted to differentiate shortly before blooming in the following season. The presence of flower was observed on current shoots derived from adventitious buds, plantlets in vitro or Diospyros sp. Deyangshi. Floral morphogenesis of‘Gongcheng Shuishi'in vitro was observed after continuous subculture using stem-segment explant. The exhibition of early flowering in Deyangshi seedling after sown three months later suggested it might enhance the transgenic or genetic research. Under the analysis of RNA-Seq data or genomic sequence, recent great advance in commercial persimmon related diploid species D. lotus revealed that the action of a Y-encoded sex determinant pseudogene called OGI (Oppressor of Me GI) , which produces small RNAs targeting the autosomal gene Me GI (Male Growth Inhibitor) , generated separated male and female individuals (dioecy, XY homomorphic) . Moreover, in hexaploid persimmon with Y-chromosome-carrying, the expression of OGI is silenced by the presence of a SINE (short interspersed nuclear element) -like insertion in the OGI promoter, named Kali. At the same time, DNA methylation of the Me GI promoter facilitates sm Me GI production to inhibit the expression of Me GI, which in turns leads to male flower development. Those gene functions were just characterized in heterogenous plants. None early flowering was observed after the regenerated transgenic shoots were sub-cultured in vitro over 2 years, which used FLOWERING LOCUS T as donor gene for transformed persimmon. Early elimination of male progeny has been regarded as an important strategy for enhancing breeding efficiency. Two male sex-linked molecular markers, Dl Sx-AF4 S and OGI locus were validated in a relatively large-scale of Diospyros L. germplasms, the accuracy of the two SCAR markers were nearly over 90%. Male plants including androecious and monoecious genotypes could be distinguished from female individiuals at an early stage. Special androecious persimmon genotypes were collected in Dabie Mountains located in central China. Those androecious genotypes presented stable male characteristics even after two consequent top-grafting. Androecious persimmon germplasm could produce high amount of pollen and its germination on stigma of leading cultivars was well. Both the outer or inner fruit quality after pollination using“Male 8”exceeded those of non-pollination. A novel pollination constant non-astringent genotype“H8-2”was derived from the artificial cross between‘Huashi 1' (pollination variant and astringent, PVA) and“Male 8”. This suggested that androecious genotype“Male 8”carries the dominant gene locus CPCNA that controls the trait of natural de-astringency. The potentiality of androecious persimmon genotypes as pollen donor for the genetic improvement of PCNA persimmon requires further investigation. This review focused on the recent development of sex determination, sex-linked molecular markers and germplasm utilization in persimmon.Systematic collection, preservation and reasonable utilization for the special germplasms with male gender should be carried out in the future.