Abstract：
The marine prasinophyte green algae Pycnococcus provasolii and Pseudoscourfieldia marina represent the only extant genera and known species of the Pycnococcaceae. However, their taxonomic status needs to be reassessed, owing to the very close relationship inferred from previous sequence comparisons of individual genes. Although Py. provasolii and Ps. marina are morphologically different, their plastid rbcL and nuclear small subunit rRNA genes were observed to be nearly or entirely identical in sequence, thus leading to the hypothesis that they represent distinct growth forms or alternate life-cycle stages of the same organism. To evaluate this hypothesis, we used organelle genomes as molecular markers. The plastome and mitogenome of Ps. marina UIO 007 were sequenced and compared with those available for two isolates of Py. provasolii (CCMP 1203 and CCAP 190/2). The Ps. marina organelle genomes proved to be almost identical in size and had the same gene content and gene order as their Py. provasolii counterparts. Single nucleotide substitutions and insertions/deletions were localized using genome-scale sequence alignments. Over 99.70% sequence identities were observed in all pairwise comparisons of plastomes and mitogenomes. Alignments of both organelle genomes revealed that Ps. marina UIO 007 is closer to Py. provasolii CCAP 190/2 than are the two Py. provasolii strains to one another. Therefore, our results are not consistent with the placement of Ps. marina and Py. provasolii strains into distinct genera. We propose a taxonomic revision of the Pycnococcaceae and the erection of a new class of Chlorophyta, the Pseudoscourfieldiophyceae.
摘要：
海洋prasinophyte绿藻Pyccoccusprovasolii和Pseudoscrafieldiamarina代表了Pycnococcaceae的唯一现存的属和已知的物种。然而,它们的分类地位需要重新评估，由于从先前的单个基因的序列比较中推断出非常密切的关系。虽然Py。provasolii和Ps。Marina在形态上不同,它们的质体rbcL和核小亚基rRNA基因在序列上几乎或完全相同，因此导致了这样的假设，即它们代表了同一生物体的不同生长形式或交替的生命周期阶段。为了评估这个假设，我们用细胞器基因组作为分子标记.PS的质体和有丝分裂体。对MarinaUIO007进行了测序，并与两个Py分离株的可用序列进行了比较。provasolii（CCMP1203和CCAP190/2）。的Ps。码头细胞器基因组被证明在大小上几乎相同，并且与它们的Py具有相同的基因含量和基因顺序。provasolii对应的。使用基因组规模序列比对定位单核苷酸取代和插入/缺失。在质体和有丝分裂基因组的所有成对比较中观察到超过99.70%的序列同一性。两个细胞器基因组的比对显示Ps。MarinaUIO007更靠近Py。CCAP原虫190/2比两个Py。provasolii菌株彼此。因此,我们的结果与Ps的放置不一致。Marina和Py.前维氏菌株分为不同的属。我们建议对Pyccocycaceae进行分类学修订，并建立了一类新的叶绿素，假天灾植物科。
