Double fertilization

Pollination

Plant reproduction

Pollen tube

Biology

Human fertilization

Gene

Germination

Ploidy

Sexual reproduction

Gametophyte

Egg cell

Pollen

Botany

Sperm

Cell biology

Genetics

Ovule

Annual Review of Plant Biology

In flowering plants, pollen tubes undergo tip growth to deliver two nonmotile sperm to the ovule where they fuse with an egg and central cell to achieve double fertilization. This extended journey involves rapid growth and changes in gene activity that manage compatible interactions with at least seven different cell types. Nearly half of the genome is expressed in haploid pollen, which facilitates genetic analysis, even of essential genes. These unique attributes make pollen an ideal system with which to study plant cell–cell interactions, tip growth, cell migration, the modulation of cell wall integrity, and gene expression networks. We highlight the signaling systems required for pollen tube navigation and the potential roles of Ca 2+ signals. The dynamics of pollen development make sexual reproduction highly sensitive to heat stress. Understanding this vulnerability may generate strategies to improve seed crop yields that are under threat from climate change.

A Fruitful Journey: Pollen Tube Navigation from Germination to Fertilization