Proteins, pollen tube growth and guidance

Pollination is a vital step for successful fertilization and seed formation in the angiosperms. Chae and Lord  outline the crucial roles of small, secreted proteins in angiosperm pollination and fertilization by highlighting recent new findings on the roles of Arabidopsis thaliana lipid transfer proteins (LTPs) and a plantacyanin in pollen-tube tip growth and chemotropic guidance, respectively. A gain-of-function mutation for Arabidopsis LTP5 (ltp5-1) disturbs polarity of tip growth, and gene over-expression of plantacyanin interferes with directionality of tube growth in the female reproductive tissues. The authors outline the significance of these plant extracellular proteins and their yet-unknown interacting partners through functional analogies from other species, such as neuronal axon guidance and mating yeast cell growth.