To achieve sexual reproduction,flowering plants have evolved a unique double fertilization system that is distinct from animals.Pollen,the male gametophyte of angiosperms,contains two immobile sperm cells and functions as a vehicle for male-female interconnection.Upon landing on the stigma of a flower,it immediately germinates and forms a highly polarized and rapidly growing pollen tube,which delivers the sperm cells to the female gametes embedded deep in the ovules (Dresselhaus et al.,2016).The communication and signaling between the pollen tube and the ovule are temporally and spatially tightly regulated at multiple steps during the growth of the pollen tube to ensure the success of the fertilization.How pollen tubes precisely target their destination and release two sperm cells on time has long puzzled biologists.Elegant studies over the past 20 years have identified that the interactions between polymorphic peptides released from the female gametes and receptors at the pollen tube surface play a leading role in attracting and targeting of pollen tubes (Okuda et al.,2009;Takeuchi and Higashiyama,2016;Wang et al.,2016).Although multiple factors for regulating pollen tube integrality have been identified,the working rationale and underlying specific mechanisms of controlling pollen tube rupture still remain elusive (Muschietti and Wengier,2017).Recently,reports on the signaling molecules leading to pollen tube burst and sperm discharge have been published (Ge et al.,2017;Mecchia et al.,2017).These studies provide a more comprehensive understanding of the process that regulates pollen tube integrity to ensure successful double fertilization in plants,and have advanced our knowledge regarding the complexity of the signaling interactions between plant male and female gametes.