Genetics, cytology, and crossing behavior of an alfalfa (Medicago sativa) mutant resulting in failure of the postmeiotic cytokinesis

Abstract

During pollen investigations on diploid alfalfa (Medicago sativa L.) several plants were identified which produced "jumbo" pollen. The cause of the jumbo pollen is failure of the postmeiotic cytokinesis. These plants produce a single, four-nucleate microspore from one microspore mother cell (MMC) rather than the normal four, single-nucleate microspores from one MMC. Subsequent gametophyte development is characterized by fusion of the four nuclei into a single nucleus in most cases (range of 80 to 100%), followed by a developmental sequence comparable to normal alfalfa. Mature 4n male gametophytes are thus formed from 2n sporophytes. Genetic control of the postmeiotic cytokinesis failure is by a single recessive gene, designated jp. Although a low frequency of jumbo pollen does germinate (range of 3.1 to 37.8%), crossing studies demonstrate jumbo pollen is incapable of effecting fertilization. The use of the jp mutant in breeding studies, and interspecific hybridization research, is discussed.

Meiosis-Driven Genome Variation in Plants

“…For example, the wheat msg gene [165], barley tri gene [171], and maize el gene [172] were found to condition the formation of unreduced eggs, but not to affect the formation of normal haploid male gametes (sperm). In diploid alfalfa (Medicago sativa), two single recessive genes, rp (restitution pollen) and jp (jumbo pollen), condition 2n pollen formation by disorientation of spindles at metaphase II and failure of cytokinesis at the second division [173,174]. In the cultivated potato (Solanum tuberosum) and related diploid Solanum species, meiotic restitution appears to be associated with asynapsis and desynapsis [129,175], abnormal spindle orientation at the second division [175][176][177], and abnormal cytokinesis [177].…”

A statistical approach to estimate the frequency of n, 2n and 4n pollen grains in diploid alfalfa

“…Results of fitting observed distributions with type A (x pollen grains from normal diploids), B (x and 2x pollen grains, the latter coming from normal tetraploids) and C (x, 2x and 4x pollen, the latter coming from jumbo pollen mutants) reference distributions / = Goodness of fit was not tested due to the lack of degrees of freedom . Smith, 1983 ;Pfeiffer & Bingham 1983) . The cytological mechanism which determines the presence of 4n pollen grains in plants producing unreduced pollen grains should be the same .…”

“…In perennial rye-grass Jansen & den Nijs (1990) used a statistical system based on fitting logtransformed data with two, three or four normal densities in order to estimate proportions of n, 2n and 4n pollen grains . This paper illustrates a different statistical approach which could be carried out because our previous research on diploid alfalfa led to the identification of 5 plants producing only 4n pollen grains (jumbo pollen), a mutation which is controlled by a single recessive gene (McCoy and Smith 1983) .…”

Sexual polyploidization in red clover

“…In nature, most if not all polyploids have arisen by sexual polyploidization through unreduced (2n) gametes (De Wet, 1982;Ramanna, 1992;Ramsey & Schemske, 1998), which production is genetically controlled (Bretagnolle & Thompson, 1995) and have been reported in cultivated plants such as Alstroemeria , potato (Peloquin et al, 1992;Ramanna & Jacobsen, 1992), sweet potato (LopezLavalle & Orjeda, 2002), alfalfa (Vorsa & Bingham, 1979;McCoy & Smith, 1983;Mariani et al, 1992;Barcaccia et al, 2003), ryegrass (Wagenvoort & Den Nijs, 1992), white clover (Hussain & Williams, 1997), red clover (Parrott & Smith, 1984;Parrott et al, 1985;Mousset-Déclas et al, 1992, Simioni et al, 2004, Rosa hybrida (Crespel & Gudin, 2003), among others.…”