The making of gametes in higher plants

Higher plants have evolved to be one of the predominant life forms on this planet. A great deal of this evolutionary success relies in a very short gametophytic phase which underlies the sexual reproduction cycle. Sexual plant reproduction takes place in special organs of the flower. In most species the processes of gametogenesis, pollination, syngamy and embryogenesis are sequentially coordinated to give rise to a functional seed in a matter of few weeks. Any of these processes is so intricately complex and precisely regulated that it becomes no wonder that each involves more specific genes and cellular processes than any other function in the plant life cycle. While variability generation - the evolutionary output of the sexual cycle - is the same as in any other Kingdom, plants do it using a completely original set of mechanisms, many of which are not yet comprehended. In this paper, we cover the fundamental features of male and female gametogenesis. While the physiological and cellular bases of these processes have been continuously described since the early nineteen century, recent usage of Arabidopsis and other species as central models has brought about a great deal of specific information regarding their genetic regulation. Transcriptomics has recently enlarged the repertoire and pollen became the first gametophyte to have a fully described transcriptome in plants. We thus place special emphasis on the way this newly accumulated genetic and transcriptional information impacts our current understanding of the mechanisms of gametogenesis.