Ovule formation is essential for realizing crop yield because it determines seed number. The underlying molecular mechanism, however, remains elusive. Here, we show that cell wall invertase (CWIN) functions as a positive regulator of ovule initiation in Arabidopsis (Arabidopsis thaliana). In situ hybridization revealed that CWIN2 and CWIN4 were expressed at the placenta region where ovule primordia initiated. Specific silencing of CWIN2 and CWIN4 using targeted artificial microRNA driven by an ovule-specific SEEDSTICK promoter (pSTK) resulted in a substantial reduction of CWIN transcript and activity, which blocked ovule initiation and aggravated ovule abortion. There was no induction of carbon (C) starvation genes in the transgenic lines, and supplementing newly forming floral buds with extra C failed to recover the ovule phenotype. This indicates that suppression of CWIN did not lead to C starvation. A group of hexose transporters was downregulated in the transgenic plants. Among them, two representative ones were spatially coexpressed with CWIN2 and CWIN4, suggesting a coupling between CWIN and hexose transporters for ovule initiation. RNA-sequencing analysis identified differentially expressed genes encoding putative extracellular receptor-like kinases, MADS-box transcription factors, including STK, and early auxin response genes in response to CWIN-silencing. Our data demonstrate the essential role of CWIN in ovule initiation, which is most likely to occur through sugar signaling instead of C nutrient contribution. We propose that CWIN-mediated sugar signaling may be perceived by, and transmitted through, hexose transporters or receptor-like kinases to regulate ovule formation by modulating downstream auxin signaling and MADS-box transcription factors.

胚珠形成对于实现作物产量至关重要，因为它决定了种子数量。然而，潜在的分子机制仍然难以捉摸。在这里，我们显示细胞壁转化酶（CWIN）充当拟南芥（Arabidopsis thaliana）胚珠起始的正调节剂。原位杂交揭示CWIN2和CWIN4在胚珠原基启动的胎盘区域表达。使用由胚珠特异性SEEDSTICK启动子（pSTK）驱动的靶向人工microRNA对CWIN2和CWIN4进行特异性沉默）导致CWIN转录本和活性大大降低，从而阻止了胚珠的启动并加剧了胚珠的流产。在转基因品系中没有碳（C）饥饿基因的诱导，并且用额外的C补充新形成的花蕾无法恢复胚珠表型。这表明抑制CWIN不会导致C饥饿。在转基因植物中一组己糖转运蛋白被下调。其中，两个代表性的蛋白在空间上与CWIN2和CWIN4共表达，表明CWIN和己糖转运蛋白之间可发生胚珠偶联。RNA测序分析确定了差异表达的基因，该基因编码假定的细胞外受体样激酶，MADS-box转录因子，包括STK和早期生长素应答基因，以响应CWIN沉默。我们的数据证明了CWIN在胚珠启动中的重要作用，而胚珠最有可能通过糖信号传递而不是C营养素贡献来发生。我们建议CWIN介导的糖信号可能被己糖转运蛋白或受体样激酶感知并通过其传播，以通过调节下游生长素信号传导和MADS-box转录因子来调节胚珠形成。