Leibniz Institute of Marine Sciences at Kiel University IFM-GEOMAR, Kiel, Germany.
BMC Genomics. 2010 Dec 20;11:718. doi: 10.1186/1471-2164-11-718.
Although the importance and widespread occurrence of iron limitation in the contemporary ocean is well documented, we still know relatively little about genetic adaptation of phytoplankton to these environments. Compared to its coastal relative Thalassiosira pseudonana, the oceanic diatom Thalassiosira oceanica is highly tolerant to iron limitation. The adaptation to low-iron conditions in T. oceanica has been attributed to a decrease in the photosynthetic components that are rich in iron. Genomic information on T. oceanica may shed light on the genetic basis of the physiological differences between the two species.
The complete 141790 bp sequence of the T. oceanica chloroplast genome [GenBank: GU323224], assembled from massively parallel pyrosequencing (454) shotgun reads, revealed that the petF gene encoding for ferredoxin, which is localized in the chloroplast genome in T. pseudonana and other diatoms, has been transferred to the nucleus in T. oceanica. The iron-sulfur protein ferredoxin, a key element of the chloroplast electron transport chain, can be replaced by the iron-free flavodoxin under iron-limited growth conditions thereby contributing to a reduction in the cellular iron requirements. From a comparison to the genomic context of the T. pseudonana petF gene, the T. oceanica ortholog can be traced back to its chloroplast origin. The coding potential of the T. oceanica chloroplast genome is comparable to that of T. pseudonana and Phaeodactylum tricornutum, though a novel expressed ORF appears in the genomic region that has been subjected to rearrangements linked to the petF gene transfer event.
The transfer of the petF from the cp to the nuclear genome in T. oceanica represents a major difference between the two closely related species. The ability of T. oceanica to tolerate iron limitation suggests that the transfer of petF from the chloroplast to the nuclear genome might have contributed to the ecological success of this species.
尽管铁限制在当代海洋中的重要性和广泛发生已得到充分证明，但我们对浮游植物适应这些环境的遗传适应性仍然知之甚少。与近岸种塔玛亚历山大藻相比，大洋种海链藻对铁限制具有高度的耐受性。海链藻对低铁条件的适应归因于富含铁的光合作用组件的减少。海链藻的基因组信息可能揭示了这两个物种之间生理差异的遗传基础。
从大规模平行焦磷酸测序（454）测序中组装的海链藻叶绿体基因组[GenBank：GU323224]的全长 141790bp，表明编码铁氧还蛋白的 petF 基因，该基因在塔玛亚历山大藻和其他硅藻中定位于叶绿体基因组中，已转移到海链藻的核中。铁硫蛋白铁氧还蛋白是叶绿体电子传递链的关键元件，在缺铁生长条件下可以被无铁黄素取代，从而减少细胞对铁的需求。通过与塔玛亚历山大藻 petF 基因的基因组背景比较，可以追溯到海链藻同源基因的起源。与塔玛亚历山大藻和菱形藻相比，海链藻叶绿体基因组的编码潜力相当，尽管在与 petF 基因转移事件相关的重排相关的基因组区域出现了一个新的表达 ORF。
海链藻 petF 从 cp 到核基因组的转移代表了这两个密切相关物种之间的主要差异。海链藻耐受铁限制的能力表明，petF 从叶绿体向核基因组的转移可能有助于该物种的生态成功。
