LAUSR

Double fertilization is an innovative phenomenon in angiosperms, in which one sperm cell first fuses with the egg cell to produce the embryo, and then the other sperm fuses with the central cell to produce the endosperm. However, the molecular mechanism of the preferential fertilization of egg cells is poorly understood. In this study, we report that two egg cell-secreted aspartic proteases, ECS1 and ECS2, play an important role in promoting preferential fertilization of egg cells in Arabidopsis. We show that simultaneous loss of ECS1 and 2 function resulted in an approximate 20% reduction in fertility, which can be complemented by the full-length ECS1/2 but not by corresponding active site mutants or by secretion-defective versions of ECS1/2. Detailed phenotypic analysis revealed that the egg cell-sperm cell attachment was compromised in ecs1 ecs2 siliques. Limited pollination assays with cdka;1 pollen showed that preferential egg cell fertilization was impaired in the ecs1 ecs2 mutant. Taken together, these results demonstrate that egg cells secret two aspartic proteases, ECS1 and ECS2, to facilitate the attachment of sperm cells to egg cells so that preferential fertilization of egg cells is achieved. This study reveals the molecular mechanism of preferential fertilization in Arabidopsis thaliana. This article is protected by copyright. All rights reserved.