Pollen-expressed RLCKs control pollen tube burst.

ABSTRACT

In angiosperms, the pollen tube enters the receptive synergid cell, where it ruptures to release its cytoplasm along with two sperm cells. This interaction is complex, and the exact signal transducers that trigger the bursting of pollen tubes are not well understood. In this study, we identify three homologous receptor-like cytoplasmic kinases (RLCKs) expressed in pollen tubes of Arabidopsis, Delayed Burst 1/2/3 (DEB1/2/3), which play a crucial role in this process. These genes produce proteins localized on the plasma membrane, and their knockout causes delayed pollen tube burst and entrance of additional pollen tubes into the embryo sac due to fertilization recovery. We show that DEBs interact with the Ca2+ pump ACA9, influencing the dynamics of cytoplasmic Ca2+ in pollen tubes through phosphorylation. These results highlight the importance of DEBs as key signal transducers and the critical function of the DEB-ACA9 axis in timely pollen tube burst in synergids.