Self-incompatibility (SI) substantially restricts the yield and quality of citrus. Therefore, breeding and analyzing self-compatible germplasm is of great theoretical and practical significance for citrus. Here, we focus on the mechanism of a self-compatibility mutation in ‘Guiyou No. 1’ pummelo (Citrus maxima), which is a spontaneous mutant of ‘Shatian’ pummelo (Citrus maxima, self-incompatibility). The rate of fruit set and the growth of pollen tubes in the pistil confirmed that a spontaneous mutation in the pistil is responsible for the self-compatibility of ‘Guiyou No. 1’. Segregation ratios of the S genotype in F1 progeny, expression analysis, and western blotting validated that the reduced levels of S2-RNase mRNA contribute to the loss of SI in ‘Guiyou No. 1’. Furthermore, we report a phased assembly of the ‘Guiyou No. 1’ pummelo genome and obtained two complete and well-annotated S haplotypes. Coupled with an analysis of SV variations, methylation levels, and gene expression, we identified a candidate gene (CgHB40), that may influence the regulation of the S2-RNase promoter. Our data provide evidence that a mutation that affects the pistil led to the loss of SI in ‘Guiyou No. 1’ by influencing a poorly understood mechanism that affects transcriptional regulation. This work significantly advances our understanding of the genetic basis of the SI system in citrus and provides information on the regulation of S-RNase genes.

中文翻译：

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S2-RNase的下调表达减弱了“桂优一号”柚的自交不亲和性

自交不亲和性（SI）极大地限制了柑橘的产量和质量。因此，自交亲和种质资源的选育与分析对柑橘具有重要的理论意义和现实意义。在这里，我们重点研究'桂优一号'柚中自交亲和突变的机制（柑橘最大值），它是“沙田”柚的自发突变体（柑橘最大值，自不兼容）。座果率和雌蕊花粉管的生长证实了'桂优1号'自交亲和的原因是雌蕊的自发突变。的分离率小号F基因型1子代、表达分析和蛋白质印迹证实，降低的小号2-核糖核酸酶mRNA导致'桂优1号'中SI的丢失。此外，我们报告了'桂优一号'柚子基因组的分阶段组装，并获得了两个完整且注释良好的小号单倍型。结合对 SV 变异、甲基化水平和基因表达的分析，我们确定了一个候选基因（CgHB40），这可能会影响监管小号2-核糖核酸酶发起人。我们的数据提供的证据表明，影响雌蕊的突变通过影响影响转录调控的知之甚少的机制，导致“桂油 1 号”中 SI 的丢失。这项工作显着提高了我们对柑橘 SI 系统遗传基础的理解，并提供了有关调控柑橘 SI 系统的信息。S-RNase基因。