Ryushiro D. Kasahara

By Ryushiro Dora Kasahara

Pollination, or the first contact between male and female gametophytes, is one of the most important steps in plant reproduction. After pollination, the pollen grains, male gametophytes, are hydrated and then germinate pollen tubes. The pollen tube initially penetrates and grows through the intercellular spaces of the stigma and then grows through the transmitting tract to the placenta connected to an ovule. The pollen tube grows along the surface of the ovule’s funiculus, through the micropyle, and into the female gametophyte. After the pollen tube enters the female gametophyte, it ruptures and releases two sperm cells with its contents. The two sperm cells then move toward and fuse with the egg cell and central cell to produce embryo and endosperm, respectively. Multiple sperm cells typically strive to “win the race” and fertilize an egg cell during animal fertilization; however, in flowering plants, each ovule harboring an egg cell generally encounters only one of many pollen tubes conveying plant sperm cells. This chapter mainly addresses reproductive strategies of plants following pollination from the pollen tube extension and the guidance of two sperm cells to the female gametophyte for fertilization in the ovule.

Part of the book: Pollination in Plants

By Xiaoyan Liu and Ryushiro D. Kasahara

Reproduction refers to the biological process of producing offspring. Sexual reproduction in angiosperms is a complex and precise process of regulation, which requires the mutual recognition of male and female gametes. The pollen tube, as a medium for transmission of male gametes, is attracted by chemoattractant derived from synergid cells in a target ovule. We first identified that MYB98 plays an important role in pollen tube guidance by regulating the downstream LURE peptides. Moreover, we discovered that if the first pollen tube penetrates the ovule but fertilization fails, the second pollen tube is attracted by another synergid cell to increase the chances of fertilization as a “wise” back-up system (Fertilization Recovery System). Similar feedback mechanisms also occur to seed development after the pollen tube guidance. We further identified a phenomenon, the pollen tube-dependent ovule enlargement morphology (POEM), that the pollen tube contents (PTCs) enlarge ovules and initiate seed coat formation without fertilization. Furthermore, we identified the POEM in rice by knocked-out GCS1 genes in rice genome, which led to fertilization failure and to produce enlarged sugar grain. In this chapter, we discuss from the reproductive strategies of the plants to the agricultural application based on our previous discoveries.

Part of the book: Plant Physiology Annual Volume 2023