International Journal of Horticulture, 2024, Vol.14, No.6, 438-450 http://hortherbpublisher.com/index.php/ijh 439 and industrial applications (Wang and Zhang, 2017; Du et al., 2023). The availability of high-quality genome sequences for both male and female E. ulmoides individuals provides a robust framework for studying the genetic basis of sex determination in this species (Du et al., 2023). Comparative transcriptome analyses have identified differentially expressed genes (DEGs) between male and female plants, highlighting potential sex-associated genes and pathways (Wang and Zhang, 2017; Zhang et al., 2023). These unique characteristics make E. ulmoides an ideal model for investigating the molecular mechanisms underlying sex differentiation in dioecious plants. This study delves into the genetic and molecular mechanisms of sex determination in E. ulmoides using high-quality genome sequences and transcriptome data, identifying key genes and pathways that regulate sexual dimorphism in this species. The study elucidates the evolutionary patterns of dioecious plants and clarifies the role of specific genes, such as MADS-box transcription factors, in sex differentiation. This study provides new insights into the mechanisms of sex determination in dioecious plants and offers a scientific basis for the development of improved breeding strategies for economically important dioecious crops. 2 Mechanisms of Sex Determination in Dioecious Plants 2.1 Genetic basis of sex determination In dioecious plants, sex determination often involves complex chromosomal mechanisms (Kazama et al., 2023). For instance, Eucommia ulmoides has been shown to possess distinct sex chromosomes, with the female genome assembly consisting of 17 pseudochromosomes and the male genome showing significant differences in size and gene content (Du et al., 2023) (Table 1). The evolution of sex chromosomes in dioecious plants can follow various pathways, including the classical model where two sex-determining genes become linked in a sex-determining region (SDR), leading to recombination suppression and chromosome differentiation. However, recent studies suggest that single genes can also act as master regulators of sex determination, as seen in species like Populus and Diospyros (Renner and Müller, 2021). Table 1 Summary of the Eucommia ulmoides genome (Adopted from Du et al., 2023) Type FemaleV1 MaleV2 MaleV1 Genome size 1.01Gb 1.24Gb 1.18Gb ContigN50 1.33Mb 17.06Kb 17.06Kb Scaffold N50 5.31Mb 1.03Mb 1.03Mb SuperScaffold N50 51.89Mb 48.30Mb 1.88Mb GCcontent 35.14% 35.19% 90% Complete BUSCOs 93.2% 92.1% 26 732 Protein coding genes 31 665 37 998 - Mean gene length 6 273bp 6199bp 1 001 Mean coding sequence length 1 086bp 1007bp 4.74 Mean number of exons per gene 5.18 4.45 211 bp Mean exon length 209 bp 226bp 61.24% Total repetitive sequence 68.26% 62.25% 3 201 Total non-coding RNAs 2 488 2865 MaleV1 Gene expression and regulation play crucial roles in the sex determination of dioecious plants. In Eucommia ulmoides, transcriptome analysis has identified key genes such as EuAP3 and EuAG that are involved in regulating sex differentiation (Du et al., 2023). MADS-box transcription factors, particularly B-class genes like EuMADS39, have been found to exhibit sex-biased expression, indicating their significant role in the genetic regulation of sex in E. ulmoides (Zhang et al., 2023). Additionally, comparative transcriptome analyses have revealed differentially expressed genes (DEGs) between male and female individuals, further highlighting the importance of gene regulation in sex determination (Wang and Zhang, 2017). In persimmon, sex determination is controlled by a pair of genes called OGI and MeGI (Figure 1), OGI is a Y-specific sex determination gene that produces non-coding hairpin formation Rnas and ultimately smRNA molecules that target homologous MeGI
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