Sex types of papaya are controlled by a pair of nascent sex chromosomes, but molecular genetic mechanisms of sex determination and sex differentiation in papaya are still unclear. We performed comparative analysis of transcriptomic profiles of male and female floral buds at the early development stage before the initiation of reproductive organ primordia at which there is no morphological difference between male and female flowers. A total of 1734 differentially expressed genes (DEGs) were identified, of which 923 showed female-biased expression and 811 showed male-biased expression. Functional annotation revealed that genes related to plant hormone biosynthesis and signaling pathways, especially in abscisic acid and auxin pathways, were overrepresented in the DEGs. Transcription factor binding motifs, such as MYB2, GAMYB, and AP2/EREBP, were enriched in the promoters of the hormone-related DEGs, and transcription factors with those motifs also exhibited differential expression between sex types. Among these DEGs, we also identified 11 genes in the non-recombining region of the papaya sex chromosomes and 9 genes involved in stamen and carpel development. Our results suggested that sex differentiation in papaya may be regulated by multiple layers of regulation and coordination and involved transcriptional, epigenetic, and phytohormone regulation. Hormones, especially ABA and auxin, transcription factors, and genes in the non-recombination region of the sex chromosome could be involved in this process. Our findings may facilitate the elucidation of signal transduction and gene interaction in sex differentiation of unisexual flowers in papaya.

中文翻译：

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木瓜花性别分化早期激素相关基因的性别偏向表达

木瓜的性别类型由一对新生的性染色体控制，但木瓜性别决定和性别分化的分子遗传机制仍不清楚。我们在生殖器官原基开始之前的早期发育阶段对雄性和雌性花芽的转录组谱进行了比较分析，此时雄性和雌性花之间没有形态差异。共鉴定出1734个差异表达基因（DEG），其中923个表现出女性偏向表达，811个表现出男性偏向表达。功能注释显示，与植物激素生物合成和信号通路相关的基因，尤其是脱落酸和生长素通路中的基因，在 DEG 中的比例过高。转录因子结合基序，例如 MYB2、GAMYB 和 AP2/EREBP，富含激素相关DEG的启动子，具有这些基序的转录因子在性别类型之间也表现出差异表达。在这些DEGs中，我们还鉴定了11个位于番木瓜性染色体非重组区的基因和9个参与雄蕊和心皮发育的基因。我们的研究结果表明，木瓜的性别分化可能受到多层调控和协调的调控，涉及转录、表观遗传和植物激素调控。激素，尤其是 ABA 和生长素、转录因子和性染色体非重组区的基因可能参与了这一过程。我们的研究结果可能有助于阐明木瓜单性花性别分化中的信号转导和基因相互作用。