Wang Yixing, Jha Ajay K, Chen Rujin, Doonan John H, Yang Ming
Department of Botany, Oklahoma State University, Stillwater, Oklahoma 74078, USA.
Genesis. 2010 Apr;48(4):254-63. doi: 10.1002/dvg.20610.
Formation of polyploid organisms by fertilization of unreduced gametes in meiotic mutants is believed to be a common phenomenon in species evolution. However, not well understood is how species in nature generally exist as haploid and diploid organisms in a long evolutionary time while polyploidization must have repeatedly occurred via meiotic mutations. Here, we show that the ploidy increased for two consecutive generations due to unreduced but viable gametes in the Arabidopsis cyclin a1;2-2 (also named tardy asynchronous meiosis-2) mutant, but the resultant octaploid plants produced progeny of either the same or reduced ploidy via genomic reductions during meiosis and pollen mitosis. Ploidy reductions through sexual reproduction were also observed in independently generated artificial octaploid and hexaploid Arabidopsis plants. These results demonstrate that octaploid is likely the maximal ploidy produced through sexual reproduction in Arabidopsis. The polyploidy-associated genomic instability may be a general phenomenon that constrains ploidy levels in species evolution.
减数分裂突变体中未减数配子受精形成多倍体生物被认为是物种进化中的常见现象。然而，目前尚不清楚的是，在漫长的进化过程中，自然界中的物种普遍以单倍体和二倍体形式存在，而多倍体化必然通过减数分裂突变反复发生。在这里，我们表明，由于拟南芥细胞周期蛋白a1;2-2（也称为迟缓异步减数分裂-2）突变体中存在未减数但可育的配子，连续两代的倍性增加，但由此产生的八倍体植物在减数分裂和花粉有丝分裂过程中通过基因组减少产生了与亲代相同或倍性降低的后代。在独立产生的人工八倍体和六倍体拟南芥植物中也观察到了通过有性生殖导致的倍性降低。这些结果表明，八倍体可能是拟南芥通过有性生殖产生的最大倍性。多倍体相关的基因组不稳定性可能是一种普遍现象，它在物种进化中限制了倍性水平。
