College of Horticulture, South China Agricultural University, Guangzhou, China.
Institute of Vegetable Research, Guangxi Academy of Agricultural Sciences, Nanning, China.
PLoS One. 2020 Aug 6;15(8):e0235962. doi: 10.1371/journal.pone.0235962. eCollection 2020.
Wild relatives represent a source of variation for many traits of interest for eggplant (Solanum melongena) breeding, as well as for broadening its genetic base. However, interspecific hybridization with wild relatives has been barely used in eggplant breeding programs, and reproductive barriers have resulted in reduced seed numbers in interspecific combinations. The mechanism underlying this phenomenon remains unclear. We hybridized females of cultivated eggplant 177 (Solanum melongena) with males of wild relatives 53 and Y11 (Solanum aethiopicum). Self-crossed 177 was the control. The seed number per control fruit was significantly higher than that of the hybrids. Paraffin sections showed no significant difference between control and 177×53 and 177×Y11. Double fertilization began 4 days post-pollination. Sperm cells were fused with egg cells 6 days post-pollination. To understand the differences in molecular mechanisms underlying this process, transcriptomes of ovaries at 0, 4, and 6 days after self-crossing and hybridization were analyzed. We screened 22,311 differentially expressed genes (DEGs) between the control and hybrids 4 and 6 days post-pollination. A total of 497 DEGs were shared among all pollination combinations. These DEGs were enriched in plant hormone transduction, cell senescence, metabolism, and biosynthesis pathways. DEG clustering analysis indicated distinct expression patterns between the control and hybrids but not between the hybrids. The DEGs in hybrids involved secondary metabolic process, phenylpropanoid metabolic process, and carboxypeptidase activity, while those in the control involved xyloglucan metabolic process, auxin-activated signaling pathway, cell wall polysaccharide metabolic process, and xyloglucosyl transferase activity. Additionally, 1683 transcription factors, including members of the AP2-ERF, MYB, bHLH, and B3 families may play important roles in self-crossing and hybridization. Our results provide insights into the regulatory mechanisms underlying variations between ovaries of self-crossed and hybrid eggplants and a basis for future studies on crossbreeding Solanum and genetic mechanisms underlying double fertilization.
野生近缘种为茄子（Solanum melongena）的许多性状提供了变异来源，也为其遗传基础的拓宽提供了可能。然而，种间杂交在茄子的育种计划中几乎没有被使用，生殖障碍导致种间组合中的种子数量减少。这种现象的机制尚不清楚。我们将栽培茄子 177（Solanum melongena）的雌性与野生近缘种 53 和 Y11（Solanum aethiopicum）的雄性进行杂交。自交的 177 作为对照。对照果实中的种子数量明显高于杂种。石蜡切片显示对照和 177×53 及 177×Y11 之间没有显著差异。授粉后 4 天开始双受精。授粉后 6 天，精子细胞与卵细胞融合。为了了解这一过程中分子机制的差异，我们分析了自交和杂交授粉后 0、4 和 6 天卵巢的转录组。我们筛选出授粉后 4 天和 6 天对照和杂种之间差异表达的基因（DEGs）有 22311 个。所有授粉组合中共有的总共有 497 个 DEGs。这些 DEGs 富集在植物激素转导、细胞衰老、代谢和生物合成途径中。DEG 聚类分析表明，对照和杂种之间的表达模式不同，但杂种之间没有差异。杂种中的 DEGs 涉及次生代谢过程、苯丙烷代谢过程和羧肽酶活性，而对照中的 DEGs 涉及木葡聚糖代谢过程、生长素激活信号通路、细胞壁多糖代谢过程和木葡聚糖转移酶活性。此外，包括 AP2-ERF、MYB、bHLH 和 B3 家族成员在内的 1683 个转录因子可能在自交和杂交中发挥重要作用。我们的研究结果为茄子自交和杂交卵巢之间变异的调控机制提供了深入了解，并为进一步研究茄子杂交和双受精遗传机制提供了基础。
