Asynchronous expression of duplicate genes in angiosperms may cause apomixis, bispory, tetraspory, and polyembryony
Asynchronous expression of duplicate genes in angiosperms may cause apomixis, bispory, tetraspory, and polyembryony
复制标题
DOI：
10.1111/j.1095-8312.1997.tb01778.x
复制
发表时间：
1997-05
影响因子：
1.9
通讯作者：
J. Carman
中科院分区：
文献类型：
--
作者：
J. Carman
产生未减数孤雌生殖卵的无融合生殖体通常是多倍体，在460个被子植物科中至少有33个。这些无融合生殖体的胚囊由不减数分裂的大孢子母细胞（二倍体孢子形成）或相邻的体细胞（无孢子形成）早熟形成。多孢子种（双孢子和四孢子）是有性的，至少存在于88个科中。它们的胚囊也早熟形成，但只有减数分裂的非关键部分受到影响。据推测，（i）在无融合生殖和多孢子生殖的物种中，胚囊形成部分或完全取代减数分裂是由控制雌性发育的重复基因的错误表达引起的，（ii）重复基因是由多倍性或古多倍性引起的（具有来自多个基因组的染色质的二倍化的多倍性），（iii）无融合生殖由几乎完整的一组错误表达的重复基因之间的竞争引起，和（iv）多孢子和多胚是由不完整的重复表达基因组之间的竞争引起的。系统发育和基因组研究进行了评估这一假设。无融合生殖、多孢子和多胚物种倾向于同时出现在雌性发育随时间变化的世界性家族中，无融合生殖通常是多倍体，每个基因组染色体数很少（X = 9.6pL0.4 SE），多孢子和多胚物种是古多倍体，每个基因组染色体数较多（分别为x= 15.7pL0.6和13.2pL0.4）。这些发现支持了所提出的重复基因重复假说，并进一步表明无融合生殖中的无性生殖保留了初级基因组，多孢和多胚多倍体中的有性生殖加速了古多倍化，并且古多倍化有时可能消除了无融合生殖所需的基因重复，而保留了多孢或多胚所需的重复。因此，无融合生殖，其长期的生殖稳定性，偶尔可能会作为一个进化的跳板，在正常的和发展新的古多倍体有性种和属的进化。
Apomicts that produce unreduced parthenogenetic eggs are generally polyploid and occur in at least 33 of 460 families of angiosperms. Embryo sacs of these apomicts form precociously from ameiotic megaspore mother cells (diplospory) or adjacent somatic cells (apospory). Polysporic species (bisporic and tetrasporic) are sexual and occur in at least 88 families. Their embryo sacs also form precociously, but only non-critical portions of meiosis are affected. It is hypothesized that (i) the partial to complete replacement of meiosis by embryo sac formation in apomictic and polysporic species results from asynchronously-expressed duplicate genes that control female development, (ii) duplicate genes result from polyploidy or paleopolyploidy (diploidized polyploidy with chromatin from multiple genomes), (iii) apomixis results from competition between nearly complete sets of asynchronously-expressed duplicate genes, and (iv) polyspory and polyembryony result from competition between incomplete sets of asynchronously-expressed duplicate genes. Phylogenetic and genomic studies were conducted to evaluate this hypothesis. Apomictic, polysporic, and polyembryonic species tended to occur together in cosmopolitan families in which temporal variation in female development is expected, apomicts were generally polyploid with few chromosomes per genome (X = 9.6pL0.4 SE), and polysporic and polyembryonic species were paleopolyploid with many chromosomes per genome (x= 15.7pL0.6 and 13.2pL0.4, respectively). These findings support the proposed duplicate-gene asynchrony hypothesis and further suggest asexual reproduction in apomicts preserves primary genomes, sexual reproduction in polysporic and polyembryonic polyploids accelerates paleopolyploidization, and pa-leopolyploidization may sometimes eliminate gene duplications required for apomixis while retaining duplications required for polyspory or polyembryony. Hence, apomixis, with its long-term reproductive stability, may occasionally serve as an evolutionary springboard in the evolution of normal and developmentally-novel paleopolyploid sexual species and genera.