Poczai Péter, Hyvönen Jaakko
Finnish Museum of Natural History (Botany), University of Helsinki, Helsinki, Finland.
Dept. Biosci. (Plant Biology), University of Helsinki, Helsinki, Finland.
PLoS One. 2017 Nov 2;12(11):e0187199. doi: 10.1371/journal.pone.0187199. eCollection 2017.
Spanish moss (Tillandsia usneoides) is an epiphytic bromeliad widely distributed throughout tropical and warm temperate America. This plant is highly adapted to extreme environmental conditions. Striking features of this species include specialized trichomes (scales) covering the surface of its shoots aiding the absorption of water and nutrients directly from the atmosphere and a specific photosynthesis using crassulacean acid metabolism (CAM). Here we report the plastid genome of Spanish moss and present the comparison of genome organization and sequence evolution within Poales. The plastome of Spanish moss has a quadripartite structure consisting of a large single copy (LSC, 87,439 bp), two inverted regions (IRa and IRb, 26,803 bp) and short single copy (SSC, 18,612 bp) region. The plastid genome had 37.2% GC content and 134 genes with 88 being unique protein-coding genes and 20 of these are duplicated in the IR, similar to other reported bromeliads. Our study shows that early diverging lineages of Poales do not have high substitution rates as compared to grasses, and plastid genomes of bromeliads show structural features considered to be ancestral in graminids. These include the loss of the introns in the clpP and rpoC1 genes and the complete loss or partial degradation of accD and ycf genes in the Graminid clade. Further structural rearrangements appeared in the graminids lacking in Spanish moss, which include a 28-kb inversion between the trnG-UCC-rps14 region and 6-kb in the trnG-UCC-psbD, followed by a third <1kb inversion in the trnT sequence.
松萝铁兰（Tillandsia usneoides）是一种附生凤梨科植物，广泛分布于热带和暖温带美洲。这种植物高度适应极端环境条件。该物种的显著特征包括覆盖其茎表面的特化毛状体（鳞片），有助于直接从大气中吸收水分和养分，以及采用景天酸代谢（CAM）的特定光合作用。在此，我们报告松萝铁兰的质体基因组，并对禾本目内的基因组组织和序列进化进行比较。松萝铁兰的质体基因组具有四分体结构，由一个大单拷贝（LSC，87,439 bp）、两个反向重复区域（IRa和IRb，26,803 bp）和一个短单拷贝（SSC，18,612 bp）区域组成。质体基因组的GC含量为37.2%，有134个基因，其中88个是独特的蛋白质编码基因，其中20个在反向重复区域中重复，这与其他已报道的凤梨科植物相似。我们的研究表明，与禾本科植物相比，禾本目早期分化的谱系没有高替换率，凤梨科植物的质体基因组显示出被认为是禾本科祖先的结构特征。这些特征包括clpP和rpoC1基因中内含子的丢失，以及禾本科分支中accD和ycf基因的完全丢失或部分降解。在松萝铁兰中缺乏的禾本科植物中出现了进一步的结构重排，包括trnG-UCC-rps14区域和trnG-UCC-psbD中的6 kb之间的28 kb倒位，随后trnT序列中出现第三个<1 kb的倒位。
