Genome elimination during microsporogenesis in two pentaploid accessions of Brachiaria decumbens (Poaceae).
Genome elimination during microsporogenesis in two pentaploid accessions of Brachiaria decumbens (Poaceae).
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DOI：
10.4238/vol9-4gmr919
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发表时间：
2010-12
期刊：
影响因子：
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通讯作者：
G. L. Ricci;M. S. Pagliarini;C. Valle
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文献类型：
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作者：
G. L. Ricci;M. S. Pagliarini;C. Valle
多倍体是植物进化中的重要力量，自古以来一直存在并持续至今。最近使用 20 世纪 80 年代从野生非洲稀树草原收集的种质对臂形草属进行的细胞遗传学研究表明，大多数物种和物种内的材料都是多倍体。已发现二倍体、四倍体和五倍体种质。我们在从非洲引入巴西的一种耐寒、入侵性牧草 Brachiaria decumbens 的两个五倍体 (2n = 5x = 45) 种质（D53 和 D71）中发现小孢子发生过程中异步减数分裂，随后基因组消除。在这些种质中，染色体在终变期间配对为 18 条二价染色体和 9 条单价染色体，表明这些种质是最近自然杂交事件的结果。基因组中染色体关联的缺乏表明这些种质是由两个不密切相关的基因型之间杂交产生的，具有低基因组亲和力和不同的减数分裂节律。九个单价染色体的减数分裂行为强化了这一假设，这些单价染色体总是落后于其他染色体，并作为小孢子中的微核被消除。这些具有奇怪水平的倍性和已证实的基因组消除的材料的行为支持多倍体材料可以通过自然杂交（新多倍化）经历新的多倍化事件的一般假设。臂形藻自然杂交的证据表明，这是一个处于持续进化过程中的野生属。
Polyploidy is a prominent and significant force in plant evolution, taking place since ancient times and continuing until today. Recent cytogenetic studies in the genus Brachiaria using germplasm collected from wild African savannas in the 1980s revealed that most species and accessions within species are polyploid. Diploid, tetraploid, and pentaploid accessions have been found. We found asynchronous meiosis during microsporogenesis, followed by genome elimination, in two pentaploid (2n = 5x = 45) accessions (D53 and D71) of a hardy, invasive pasture grass, introduced from Africa to Brazil, Brachiaria decumbens. In these accessions, chromosomes paired as 18 bivalents and nine univalents during diakinesis, suggesting that these accessions resulted from a recent event of natural hybridization. The lack of chromosome associations in the genomes suggests that these accessions resulted from hybridization between two genotypes that are not closely related, with low genome affinity and with different meiotic rhythms. This supposition is reinforced by the meiotic behavior of the nine univalents, which were always laggard in relation to the other chromosomes and eliminated as micronuclei in microspores. The behavior of these accessions, which have an odd level of ploidy and confirmed genome elimination, supports the general assumption that a polyploid accession can undergo a new event of polyploidization by natural hybridization (neopolyploidyzation). This evidence for natural hybridization in Brachiaria shows that this is a wild genus in an ongoing evolutionary process.