Gametophytic interactions during pollen tube guidance in Arabidopsis
Hongju Li, Shanshan Zhu, Yong Xue, Tong Wang, Weicai Yang^*

State Key Laboratory of Molecular Developmental Biology, and National Center for Plant Gene Research (Beijing), Institute of Genetics and Developmental Biology, Beijing, China.
^*Corresponding author: Tel/Fax: (086) 10 64807761; E-mail: wcyang@genetics.ac.cn

Abstract
Pollen tube guidance is a common process in angiosperm that involves cell-cell interactions and signaling between the male gametophyte (pollen) and the female gametophyte. The putative female cues to attract pollen tube have been shown to be Cys-rich defensin-like peptide secreted by the synergid. We previously showed that the central cell plays an important role in guidance as mutation in CCG abolishes this process. I will discuss its role and mode of action in pollen tube guidance. On the male side, nothing is known on how pollen tube perceives and responds to the female cues. In an effort to identify male mutations disrupting the perception of the female signals, we identified a pollen-specific mutation, pod1 that blocks micropylar pollen tube guidance in Arabidopsis. POD1 is an ER luminal protein that is conserved in all eukaryotic organisms and is expressed in pollen, pollen tube and the synergid of the embryo sac. POD1 interacts with Calreticulin 3, suggesting that it may act as a co-chaperone in the ER lumen. We propose that POD1 controls the folding and/or secretion of putative receptors for the female cues by modulating CNX/CRT3-mediated ER quality control in pollen tube guidance.

Key words: Pollen tube guidance, Arabidopsis, CCG, POD1, reproduction