Primordial germ cell is differentiated from hypodermis of stamen (male) and pistil (female) primordia in angiosperm species. Primordial germ cells are divided mitotically several times, and produce into meiocytes and nursery cells. Meiosis is one of the essential events of genetics, because it generates a new gene combination different from that of parents.
  It has remained to be largely unknown how flowering plants generate and maintain germ cells, and how they undergo meiosis. To answer these questions, we have analyzed molecular functions of genes and proteins relating to early steps of plant germ-cell initiation, development and/or meiosis, mainly by using mutant lines of rice, a monocotyledonous model plant. 
  We have also conducted the germplasm center of wild relatives and local varieties of rice in collaboration with the Plant Genetics Lab., under the funding support of the National Bioresource Project, Japan (NBRP).

Molecular cytologenetic analyses of germ-cell development in rice. (A) A schematic illustration of reproductive-cell development from initiation of primordial germ cells to meiosis in rice. Top and bottom drawings indicate the cross sections of an anther lobe and the longitudinal sections of ovule primordium, respectively. Red indicates primordial germ cells, orange; meiocytes. Beneath the pictures, reproduction-related genes that we have identified so far are shown. (B-E) Molecular cytogenetic analses of mel2 mutant. (B, C) In situ hybridization of MEL1 gene, the marker specific for premeiotic germ cells, to anthers at meiotic prophase I. In the wild type (B), MEL1 expression has been downregulated, and in cotrast in the mel2 mutant (C), it has been expressed strongly, indicating that mel2 germ cells fail to enter meiosis. (D, E) Immunofluorescent staining of meiotic proteins for pollen mother cells at zygotene. In the wild type (D), meiotic proteins PAIR2 (purple) and ZIP1 (green) are accumulated and loaded on homologous chromosomes, and in contrast in mel2 mutant (E), both proteins fail to load normally on chromosomes. Chromosomes are counter-stained with DAPI.