From diploids to allopolyploids: The emergence of efficientpairing control genes in plants

Polyploidy has played a major role in the evolution of higher plants. Precise control of chromosome pairing is vital for conferring meiotic regularity, and hence reproductive stability in allopolyplolds. In this review, we examine whether strong evidence has accumulated for the presence and activity of pairing control genes in different allopolyploid species that are entirely bivalent forming and that display a strict disomic inheritance. We show that very good evidence has been adduced in Traticum species, Avena sativa, Festum arundinacea, Brassica corns, Gossypium hirsutum, and G. barbadense, and in amphldlploids related to the diploid species Lolium perenne, L. multiflorum, and L. rigidum. More circumatamlal evidence has been obtained for polyploids in the genera Aegilops, Hordeum, Nicotiana, and Coffea, which have received far less attention than the other species. Although these pairing regulators seem to control different processes operating throughout the premeiotic Interphase and the meiotic prophase, little is known about their precise mode of action We present three hypotheses that have been proposed to explain the origin and evolution of pairing control genes; none of them has been supported by direct evidence, and the origin of most pairing suppressors is stili unknown. Accordingly, the study of pairing control genes is stili an Important task for understanding the stabilization and establishment of allopolyploid species.