Graduate School of Horticulture, Chiba University, Matsudo 648, Matsudo-shi 271-8510, Japan.
Graduate School of Life Sciences, Department of Ecological Developmental Adaptability Life Sciences, Tohoku University, 2-1-1 Katahira, Sendai 980-8577, Japan.
Biomolecules. 2023 Jan 20;13(2):208. doi: 10.3390/biom13020208.
In the sexual reproduction of flowering plants, two independent fertilization events occur almost simultaneously: two identical sperm cells fuse with either the egg cell or the central cell, resulting in embryo and endosperm development to produce a seed. GCS1/HAP2 is a sperm cell membrane protein essential for plasma membrane fusion with both female gametes. Other sperm membrane proteins, DMP8 and DMP9, are more important for egg cell fertilization than that of the central cell, suggesting its regulatory mechanism in GCS1/HAP2-driving gamete membrane fusion. To assess the GCS1/HAP2 regulatory cascade in the double fertilization system of flowering plants, we produced transgenic lines expressing different GCS1/HAP2 variants and evaluated the fertilization in vivo. The fertilization pattern observed in _RNAi transgenic plants implied that sperm cells over the amount of GCS1/HAP2 required for fusion on their surface could facilitate membrane fusion with both female gametes. The cytological analysis of the sperm cell arrested alone in an embryo sac supported GCS1/HAP2 distribution on the sperm surface. Furthermore, the fertilization failures with both female gametes were caused by GCS1/HAP2 secretion from the egg cell. These results provided a possible scenario of GCS1/HAP2 regulation, showing a potential scheme for capturing additional GCS1/HAP2-interacting proteins.
在有花植物的有性生殖中，两个独立的受精事件几乎同时发生：两个相同的精子细胞与卵细胞或中央细胞融合，导致胚胎和胚乳发育产生种子。GCS1/HAP2 是一种精子细胞膜蛋白，对于与两种雌性配子的质膜融合是必不可少的。其他精子膜蛋白，DMP8 和 DMP9，对于卵细胞受精比中央细胞受精更为重要，这表明其在 GCS1/HAP2 驱动配子膜融合中的调节机制。为了评估有花植物双受精系统中 GCS1/HAP2 的调节级联，我们产生了表达不同 GCS1/HAP2 变体的转基因系，并在体内评估了受精情况。在 _RNAi 转基因植物中观察到的受精模式表明，精子细胞表面的 GCS1/HAP2 量超过融合所需的量，可以促进与两种雌性配子的膜融合。在单独停留在胚囊中精子细胞的细胞学分析支持 GCS1/HAP2 在精子表面的分布。此外，与两种雌性配子的受精失败是由卵细胞中 GCS1/HAP2 的分泌引起的。这些结果提供了 GCS1/HAP2 调节的可能情景，显示了捕获额外的 GCS1/HAP2 相互作用蛋白的潜在方案。
