State Key Laboratory of Biocontrol and Guangdong Provincial Key Laboratory of Plant Resources, School of Life Sciences, Sun Yat-sen University, Guangzhou 510275, China.
IBAM, Universidad Nacional de Cuyo, CONICET, Facultad de Ciencias Agrarias & Facultad de Ciencias Exactas y Naturales, Almirante Brown 500, Chacras de Coria, M5528AHB Mendoza, Argentina.
Curr Biol. 2022 Jan 24;32(2):470-479.e5. doi: 10.1016/j.cub.2021.11.053. Epub 2021 Dec 13.
The plastid and nuclear genomes of parasitic plants exhibit deeply altered architectures, whereas the few examined mitogenomes range from deeply altered to conventional. To provide further insight on mitogenome evolution in parasitic plants, we report the highly modified mitogenome of Rhopalocnemis phalloides, a holoparasite in Balanophoraceae. Its mitogenome is uniquely arranged in 21 minicircular chromosomes that vary in size from 4,949 to 7,861 bp, with a total length of only 130,713 bp. All chromosomes share an identical 896 bp conserved region, with a large stem-loop that acts as the origin of replication, flanked on each side by hypervariable and semi-conserved regions. Similar minicircular structures with shared and unique regions have been observed in parasitic animals and free-living protists, suggesting convergent structural evolution. Southern blots confirm both the minicircular structure and the replication origin of the mitochondrial chromosomes. PacBio reads provide evidence for chromosome recombination and rolling-circle replication for the R. phalloides mitogenome. Despite its small size, the mitogenome harbors a typical set of genes and introns within the unique regions of each chromosome, yet introns are the smallest among seed plants and ferns. The mitogenome also exhibits extreme heteroplasmy, predominantly involving short indels and more complex variants, many of which cause potential loss-of-function mutations for some gene copies. All heteroplasmic variants are transcribed, and functional and nonfunctional protein-coding variants are spliced and RNA edited. Our findings offer a unique perspective into how mitogenomes of parasitic plants can be deeply altered and shed light on plant mitogenome replication.
寄生植物的质体和核基因组表现出深度改变的结构，而少数被检查的线粒体基因组则从深度改变到常规。为了进一步了解寄生植物中线粒体基因组的进化，我们报告了 Rhopalocnemis phalloides 的高度修饰的线粒体基因组，这是 Balanophoraceae 中的一种全寄生植物。它的线粒体基因组独特地排列在 21 个小型环状染色体中，大小从 4949 到 7861bp 不等，总长度仅为 130713bp。所有染色体都共享一个相同的 896bp 保守区域，具有一个大的茎环结构，作为复制起点，两侧是高度可变和半保守区域。在寄生动物和自由生活的原生动物中也观察到了具有共享和独特区域的类似小型环状结构，表明存在趋同的结构进化。Southern blot 实验证实了线粒体染色体的小型环状结构和复制起点。PacBio 读取提供了证据，证明了 R. phalloides 线粒体基因组的染色体重组和滚环复制。尽管其体积较小，但线粒体基因组在每个染色体的独特区域内仍拥有典型的基因和内含子集，但内含子是种子植物和蕨类植物中最小的。线粒体基因组还表现出极端的异质性，主要涉及短插入缺失和更复杂的变体，其中许多变体导致一些基因拷贝的潜在功能丧失突变。所有异质变体都被转录，功能和非功能的蛋白质编码变体被剪接和 RNA 编辑。我们的研究结果提供了一个独特的视角，了解寄生植物的线粒体基因组如何被深度改变，并为植物线粒体基因组复制提供了启示。
