2N POLLEN FORMATION: 40 CYTOLOGICAL MECHANISMS OF NUCLEAR MEIOTIC RESTITUTION pp. 1-64
Authors: (Nataliya V. Shamina, Institute of Chemical Biology and Experimental Medicine, Siberian Branch of RAS, Novosibirsk, Russia)
Abstract: Gametes with diploid chromosome number play a considerable role in higher plant evolution and speciation and are an important instrument in breeding (Mendiburu, Peloquin, 1976; Peloquin et al., 1999; Jauhar, 2003; Cai and Xu, 2007). In angiosperms, about 30% - 80% of species were estimated to be of polyploid origin. Polyploidisation is a key evolutionary process in higher plants that lead to the formation of new species. The majority of higher plant species evolutionised this way, or by means of hybridization with more or less widely related species and further polyploidisation. Such important phenomenon as gametophytic apomixis is also associated with polyploidy (Estrada-Luna et al., 2002; d‘Erfurth et al., 2009). Apomixis is a specific reproduction method that allows us to obtain absolute genetic copies of mother plants and is related with the process of 2n gametes formation. Despite impressive advancements of genetic engineering in development of transgenic plants, wide hybridization remains the most important and, so far, indispensible method to obtain breeding material. It is explained by the thing that most of the traits important for breeding have polygenic control and cannot be transferred by transformation. Overcoming hybrids F1 sterility is the key problem of plant wide hybridization (Udall and Wendel, 2006). Under complete or partial absence of homologs conjugation, regular chromosome distribution in two subsequent meiotic divisions becomes impossible. Developing microspores have their aneuploid chromosome number and are non-viable. Rapid development of fertile wide hybrids is possible due to sexual polyploidisation realized by 2n gametes. Such gametes form in parents or in hybrids (allohaploids) as a result of meiotic restitution process (Consiglio et al., 2004).