Biodiversity Program, Taiwan International Graduate Program, Academia Sinica and National Taiwan Normal University, Taipei, Taiwan.
Department of Life Science, National Taiwan Normal University, Taipei, Taiwan.
Genome Biol Evol. 2019 Jun 1;11(6):1691-1705. doi: 10.1093/gbe/evz059.
Acetyl-CoA carboxylase (ACCase) is the key regulator of fatty acid biosynthesis. In most plants, ACCase exists in two locations (cytosol and plastids) and in two forms (homomeric and heteromeric). Heteromeric ACCase comprises four subunits, three of them (ACCA-C) are nuclear encoded (nr) and the fourth (ACCD) is usually plastid encoded. Homomeric ACCase is encoded by a single nr-gene (ACC). We investigated the ACCase gene evolution in gymnosperms by examining the transcriptomes of newly sequenced Gnetum ula, combined with 75 transcriptomes and 110 plastomes of other gymnosperms. AccD-coding sequences are elongated through the insertion of repetitive DNA in four out of five cupressophyte families (except Sciadopityaceae) and were functionally transferred to the nucleus of gnetophytes and Sciadopitys. We discovered that, among the three genera of gnetophytes, only Gnetum has two copies of nr-accD. Furthermore, using protoplast transient expression assays, we experimentally verified that the nr-accD precursor proteins in Gnetum and Sciadopitys can be delivered to the plastids. Of the two nr-accD copies of Gnetum, one dually targets plastids and mitochondria, whereas the other potentially targets plastoglobuli. The distinct transit peptides, gene architectures, and flanking sequences between the two Gnetum accDs suggest that they have independent origins. Our findings are the first account of two distinctly targeted nr-accDs of any green plants and the most comprehensive analyses of ACCase evolution in gymnosperms to date.
乙酰辅酶 A 羧化酶（ACCase）是脂肪酸生物合成的关键调节因子。在大多数植物中，ACCase 存在于两个位置（细胞质和质体）和两种形式（同型和异型）。异型 ACCase 由四个亚基组成，其中三个（ACCA-C）是核编码的（nr），第四个（ACCD）通常是质体编码的。同型 ACCase 由单个 nr 基因（ACC）编码。我们通过检查新测序的买麻藤的转录组，结合其他 75 种裸子植物的转录组和 110 种质体基因组，研究了裸子植物中的 ACCase 基因进化。在五个柏科植物科（除南洋杉科外）中，有四个科的 AccD 编码序列通过重复 DNA 的插入而延长，并被功能转移到买麻藤和松科植物的核中。我们发现，在 3 个买麻藤属中，只有买麻藤属有两个 nr-accD 拷贝。此外，通过原生质体瞬时表达测定，我们实验验证了买麻藤和松科植物中的 nr-accD 前体蛋白可以被递送到质体中。在买麻藤的两个 nr-accD 拷贝中，一个双重靶向质体和线粒体，而另一个可能靶向质体小球体。这两个 Gnetum accD 的独特转运肽、基因结构和侧翼序列表明它们具有独立的起源。我们的研究结果是首次报道任何绿色植物的两个明显靶向 nr-accD，也是迄今为止对裸子植物中 ACCase 进化最全面的分析。
