Yi Jun, Kradolfer David, Brownfield Lynette, Ma Yingrui, Piskorz Ewa, Köhler Claudia, Jiang Hua
Department of Plant Biology, Uppsala BioCenter, Linnean Center for Plant Biology, Swedish University of Agricultural Sciences, Uppsala, SE-75007, Sweden.
Department of Biochemistry, University of Otago, Dunedin, 9054, New Zealand.
New Phytol. 2023 Feb;237(4):1179-1187. doi: 10.1111/nph.18473. Epub 2022 Dec 11.
Polyploidy, the presence of more than two sets of chromosomes within a cell, is a widespread phenomenon in plants. The main route to polyploidy is considered through the production of unreduced gametes that are formed as a consequence of meiotic defects. Nevertheless, for reasons poorly understood, the frequency of unreduced gamete formation differs substantially among different plant species. The previously identified meiotic mutant jason (jas) in Arabidopsis thaliana forms about 60% diploid (2n) pollen. JAS is required to maintain an organelle band as a physical barrier between the two meiotic spindles, preventing previously separated chromosome groups from uniting into a single cell. In this study, we characterized the jas suppressor mutant telamon (tel) that restored the production of haploid pollen in the jas background. The tel mutant did not restore the organelle band, but enlarged the size of male jas tel meiocytes, suggesting that enlarged meiocytes can bypass the requirement of the organelle band. Consistently, enlarged meiocytes generated by a tetraploid jas mutant formed reduced gametes. The results reveal that meiocyte size impacts chromosome segregation in meiosis II, suggesting an alternative way to maintain the ploidy stability in meiosis during evolution.
多倍体是指细胞内存在两套以上染色体的现象，这在植物中是一种普遍存在的现象。多倍体形成的主要途径被认为是通过产生由于减数分裂缺陷而形成的未减数配子。然而，由于尚不清楚的原因，不同植物物种中未减数配子形成的频率差异很大。先前在拟南芥中鉴定出的减数分裂突变体jason（jas）会形成约60%的二倍体（2n）花粉。JAS对于维持细胞器带作为两个减数分裂纺锤体之间的物理屏障是必需的，可防止先前分离的染色体组合并为一个细胞。在本研究中，我们鉴定了jas抑制突变体telamon（tel），它在jas背景下恢复了单倍体花粉的产生。tel突变体并未恢复细胞器带，但增大了jas tel雄性减数分裂细胞的大小，这表明增大的减数分裂细胞可以绕过对细胞器带的需求。一致地，由四倍体jas突变体产生的增大的减数分裂细胞形成了减数配子。结果表明，减数分裂细胞大小会影响减数分裂II中的染色体分离，这表明在进化过程中存在一种维持减数分裂中倍性稳定性的替代方式。
