LAQV/REQUIMTE, Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre s/n, 4169-007, Porto, Portugal.
Instituto Gulbenkian de Ciência, Rua da Quinta Grande 6, 2780-156, Oeiras, Portugal.
Plant Reprod. 2024 Sep;37(3):341-353. doi: 10.1007/s00497-024-00495-w. Epub 2024 Jan 31.
GPI anchor addition is important for JAGGER localization and in vivo function. Loss of correct GPI anchor addition in JAGGER, negatively affects its localization and function. In flowering plants, successful double fertilization requires the correct delivery of two sperm cells to the female gametophyte inside the ovule. The delivery of a single pair of sperm cells is achieved by the entrance of a single pollen tube into one female gametophyte. To prevent polyspermy, Arabidopsis ovules avoid the attraction of multiple pollen tubes to one ovule-polytubey block. In Arabidopsis jagger mutants, a significant number of ovules attract more than one pollen tube to an ovule due to an impairment in synergid degeneration. JAGGER encodes a putative arabinogalactan protein which is predicted to be anchored to the plasma membrane by a glycosylphosphatidylinositol (GPI) anchor. Here, we show that JAGGER fused to citrine yellow fluorescent protein (JAGGER-cYFP) is functional and localizes mostly to the periphery of ovule integuments and transmitting tract cells. We further investigated the importance of GPI-anchor addition domains for JAGGER localization and function. Different JAGGER proteins with deletions in predicted ω-site regions and GPI attachment signal domain, expected to compromise the addition of the GPI anchor, led to disruption of JAGGER localization in the cell periphery. All JAGGER proteins with disrupted localization were also not able to rescue the polytubey phenotype, pointing to the importance of GPI-anchor addition to in vivo function of the JAGGER protein.
GPI 锚添加对于 JAGGER 的定位和体内功能很重要。JAGGER 中正确的 GPI 锚添加的缺失，会对其定位和功能产生负面影响。在开花植物中，成功的双受精需要将两个精子细胞正确地输送到珠孔内的雌性配子体中。通过单个花粉管进入一个雌性配子体来实现单个配对的精子细胞的输送。为了防止多精入卵，拟南芥珠孔避免多个花粉管被吸引到一个珠孔-多管堵塞上。在拟南芥 jagger 突变体中，由于协同细胞退化的损伤，大量的珠孔吸引不止一个花粉管到一个珠孔中。JAGGER 编码一个假定的阿拉伯半乳聚糖蛋白，该蛋白被预测通过糖基磷脂酰肌醇（GPI）锚定到质膜上。在这里，我们表明，与 citrine 黄色荧光蛋白（JAGGER-cYFP）融合的 JAGGER 是有功能的，并且主要定位于珠孔被膜和传递道细胞的外周。我们进一步研究了 GPI 锚添加结构域对于 JAGGER 定位和功能的重要性。具有预测的 ω 位区域和 GPI 附着信号域缺失的不同 JAGGER 蛋白，预计会破坏 GPI 锚的添加，导致 JAGGER 在细胞外周的定位中断。所有定位中断的 JAGGER 蛋白也不能拯救多管堵塞表型，这表明 GPI 锚添加对于 JAGGER 蛋白的体内功能很重要。
