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Abstract The B chromosome in maize is a supernumerary chromosome that due to its dispensability is present in only some lines of maize. Over its evolution, the B chromosome has developed a two-part drive mechanism that ensures its continued presence in maize populations. Its drive mechanism involves nondisjunction at the second pollen mitosis in which two sperm cells are produced and preferential fertilization by the sperm with the two B chromosomes more often joining with the egg as opposed to the central cell in the process of double fertilization. Previous work had suggested some lines of maize exhibit a different response and that this was controlled by the female parent. We sought to examine the variation for this trait by testing a wide spectrum of characterized maize lines. Most inbred lines exhibit the canonical preference for the egg cell, some appear to have random fertilization, and one inbred line (B73) shows a preference for the B containing sperm to fertilize the central cell.
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Aneuploidy and ploidy variation conditioned by the B chromosome of maize
Abstract The supernumerary B chromosome of maize has a drive mechanism to maintain itself in a population despite being dispensible. This involves nondisjunction of the B centromere at the second pollen mitosis that produces the two sperm followed by preferential fertilization of the egg by the B containing sperm during double fertilization. During an introgression of the supernumerary B chromosome into the inbred line B73, an unusually high frequency of trisomies for A chromosomes was observed. Due to parallels to the High Loss phenomenon in which three or more B chromosomes in a specific genetic background cause chromosomal breakage at heterochromatic knob sites during the second pollen mitosis as well as ploidy changes, this phenomenon was revisited. Examination of pollen of the High Loss line revealed a high frequency of single sperm in the presence of the B chromosomes, which was previously not realized. Crosses to tetraploid females confirmed that the single sperm were diploid and functional but also revealed the presence of diploids with their A chromosomes derived solely from the tetraploid parent indicating a “diploid induction”. Collectively, the results reveal two backgrounds in which the B drive mechanism is not confined to this chromosome causing detrimental effects by adherence of heterochromatic knobs and apparently A centromeres at the mitosis preceding sperm development. In most genetic backgrounds this process is restricted to the B chromosome but in B73 and the High Loss line, there is spillover to the normal chromosomes in distinct ways.
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- Award ID(s):
- 2214243
- PAR ID:
- 10585337
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Heredity
- ISSN:
- 0018-067X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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