The angiosperm female gametophyte: No longer the forgotten generation

The plant life cycle alternates between the diploid sporophyte (spore-producing organism) and the haploid gametophyte (gamete-producing organism). The female gametophyte of flowering plants develops within the ovule, a specialized structure within the ovary, which gives rise to the seed after fertilization. The female gametophyte, or embryo sac, contains a small number of clonally derived cell types and serves as a model for the study of many fundamental processes crucial to development. The female gametophyte develops coordinately with the sporophytic tissues of the ovule, providing an ideal system to study axis determination, pattern formation, cell–cell communication, and the role of cell lineage and position in cell specification and differentiation. Despite the important role played by the gametophyte in reproduction, few studies have focused attention on the molecular or genetic aspects of female gametophyte development and function. Consequently, the gametophyte was termed 'the forgotten generation'. In this paper we illustrate the developmental and structural diversity of gametophytes, studied to a large extent by the Indian school influenced by P. Maheshwari, and review new insights gained by genetic and molecular studies.