Editorial: Molecular and Cellular Plant Reproduction

The world is now facing many severe problems due to increasing global demands for already limiting food and energy resources. Plant reproduction is crucial not only for producing offspring but also for improving crop quality and yield. Moreover, plant reproduction entails complex growth and developmental processes, which offer various opportunities for elucidating fundamental principles in biology. To provide a comprehensive update on the myriad of topics in the field of plant reproduction, we invited contributions for a Research Topic entitled " Molecular and Cellular Plant Reproduction ". After an overwhelming response, reflecting the active research being undertaken in plant reproduction, we published a total of 31 papers, including 1 hypothesis and theory, 4 perspectives, 12 reviews, and 14 original research articles. As a result, this special issue covers the broad scope and dynamics of studies on plant reproduction, ranging from a hypothesis of the sexual reproduction cycle, by floral organ degeneration and abiotic stresses. The life cycle of flowering plants features the alternation of diploid sporophyte and haploid gametophyte generations, in which a crucial step is to specify diploid reproductive cells from somatic cells. Animals generate diploid germlines during early embryonic development, while flowering plants determine reproductive cell lines post-embryonically. Bai proposes a sexual reproduction cycle (SRC) hypothesis, which generalizes sexual reproduction into an alternated three-step cycle consisting of meiosis, sex differentiation, and fertilization. In his hypothesis, Bai makes a remarkable attempt to address evolution as well as differences and similarities in sexual reproduction among various organisms, including fungi, plants, and animals. Sexual reproduction bestows selective advantages during evolution. Interestingly, Hojsgaard and Hörandl argue that " a little bit of sex " is helpful for apomictic plants to avoid genomic decay and extinction. Zhu et al. show that asexually propagated Alternanthera philoxeroides produces dysfunctional stamens due to decreased expression of B-class genes, suggesting that loss of sexual reproductive capacity might help evolution of asexual reproduction in clonal plants or vice versa.