Fertilization-Dependent Mechanism of Egg Cell Preventing Polytubey
YU Xiaobo1,2, SUN Mengxiang2*
In the process of fertilization in animals, proteases secreted from cortical granules of egg cells function to prevent polyspermy. In flowering plants, fertilization is more complex and involves a pair of non-motile sperm cells deliveres by a pollen tube, and then two sperm fuses with an egg cell and a central cell respectively. Usually, each ovule only attracts one pollen tube and thus efficiently reduces the possibility of polyspermy. However, the mechanism of plant preventing polytubey has remained unknown foe decades. Recently, it reports that the egg cell itself plays a critical role in preventing polytubey. Two aspartic proteases, ECS1 and ECS2, are specifically expressed in the egg cell and degraded soon after successful sperm-egg fusion. ECS locates at the apical domain of the Arabidopsis egg cell in the form of a cortical network. The secretion of ECS is triggered by sperm-egg fusion. The ecs1ecs2 double mutants showed polytubey phenotype. Further study reveales that ECS1 and ESC2 can cleavepollen tube attractant LURE1 specifically and thus quickly block the pollen tube attraction to prevent polytubey. These results indicate that plant egg cell can sense successful fertilization and establish a fertilization dependent mechanism to prevent polytubey.
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