The Key Laboratory for Quality Improvement of Agricultural Products of Zhejiang Province, School of Agriculture and Food Science, Zhejiang A&F University, Linan, Hangzhou, 311300, Zhejiang, China.
State Key Laboratory of Cotton Biology, Institute of Cotton Research, Chinese Academy of Agricultural Science (ICR, CAAS), Anyang, 455000, China.
Mol Genet Genomics. 2020 Jan;295(1):47-54. doi: 10.1007/s00438-019-01602-7. Epub 2019 Aug 16.
Stem trichomes and seed fibers originate from epidermal cells and partially share a regulatory pathway at the molecular level. In Gossypium barbadense, two insertions of a Ty1 long-terminal repeat-retrotransposon [transposable element TE1 and TE2] in a homeodomain-leucine zipper gene (HD1) result in glabrous stems. The primers used to identify the TE insertions in G. barbadense were applied to screen for the same events in 81 modern G. hirsutum varieties and 31 wild races. Three wild races were found carrying the same TEs as G. barbadense. However, the TE insertions in two of these wild races occurred at different sites (4th exon), therefore, named TE3, while the TE in the other wild race occurred at the same site as TE2. An RNA sequencing and qRT-PCR analysis indicated that the loss of HD1 function was caused by the TE insertion. Genetic mapping revealed a strong association between glabrous stems and TE3 insertions, confirming that HD1 is a critical gene for stem trichome initiation in G. hirsutum, as in G. barbadense. Using the long-terminal repeat sequence as a query to search against the Texas Marker-1 reference genome sequence, we found that the TE occurred after tetraploid cotton formation and evolved at different rates in G. hirsutum and G. barbadense. Interestingly, at least three independent insertion events of the same retrotransposon occurred preferentially in the A sub-genome's HD1 gene, but not in the D sub-genome of G. hirsutum or G. barbadense, suggesting that an unknown TE insertion mechanism and resultant gene function changes may have hastened cotton speciation.
茎毛和种皮纤维起源于表皮细胞，在分子水平上部分共享一个调控途径。在海岛棉中，Ty1 长末端重复反转录转座子[转座元件 TE1 和 TE2]的两个插入物导致无毛茎。用于鉴定海岛棉中 TE 插入的引物被应用于筛选 81 个现代陆地棉品种和 31 个野生种的相同事件。发现三个野生种携带与海岛棉相同的 TE。然而，其中两个野生种的 TE 插入发生在不同的位点（第 4 外显子），因此命名为 TE3，而另一个野生种的 TE 与 TE2 发生在相同的位点。RNA 测序和 qRT-PCR 分析表明，HD1 功能的丧失是由 TE 插入引起的。遗传作图显示，无毛茎与 TE3 插入之间存在强烈的关联，证实 HD1 是陆地棉茎毛起始的关键基因，就像在海岛棉中一样。使用长末端重复序列作为查询，在德克萨斯标记-1 参考基因组序列中进行搜索，我们发现 TE 发生在四倍体棉形成之后，并且在陆地棉和海岛棉中以不同的速度进化。有趣的是，同一反转录转座子的至少三个独立插入事件优先发生在 A 亚基因组的 HD1 基因中，但不在陆地棉或海岛棉的 D 亚基因组中，这表明未知的 TE 插入机制和由此产生的基因功能变化可能加速了棉花的物种形成。
