Molecular repertoire of flowering plant male germ cells

Sperm cells—the male gametes of flowering plants—constitute the male founding lineage of angiosperms, possessing the unique capacity to fuse with the egg and central cells during double fertilization. Although it is well established that these cellular fusions are involved with initiating the development of the seedling-forming zygote and the endosperm that nourishes it, considerable information will be needed to characterize the full male molecular repertoire, which includes expressed genes of the male lineage, encoded proteins, and regulatory elements controlling male germ line identity, as well as male molecules that may mediate interactions with the female partner that initiate fertilization and development. Progress is being made using increasingly sensitive molecular methods to uncover important genes. With the pace of this discovery rapidly increasing, the likely outcome is that key molecules will be discovered within the next several years that control the founding cells of the embryo and endosperm and are involved in directing early development. Further insights into the genes and gene pathways that regulate male germ line differentiation will advance not only our fundamental understanding of these reproductive cells, but also the nature of cell–cell recognition, membrane fusion, double fertilization, zygote activation, early plant development and may aid our understanding of factors that have contributed to the overwhelming evolutionary success of flowering plants.