Abstract
Ulva flexuosa, one kind of green tide algae, has outbroken in the Yellow Sea of China during the past ten years. In the present study, we sequenced the chloroplast genome of U. flexuosa followed by annotation and comparative analysis. It indicated that the chloroplast genomes had high conservation among Ulva spp., and high rearrangement outside them. Though U. flexuosa was closer to U. linza than U. fasciata in phylogenetic tree, the average Ka/Ks between U. flexuosa and U. linza assessed by 67 protein-coding genes was higher than those between U. flexuosa and other species in Ulva spp., due to the variation of psbZ, psbM and ycf20. Our results laid the foundation for the future studies on the evolution of chloroplast genomes of Ulva, as well as the molecular identification of U. flexuosa varieties.
Highlights
The macroalgae representing the cosmopolitan green algae Ulva flexuosa Wulfen species have been found in Europe since the mid-1800s [1], which are very common and regularly encountered in fresh waters, slightly saline waters, and estuaries [2], containing the characteristics of transitional species
We have: (1) sequenced the chloroplast genome of U. flexuosa; (2) annotated the chloroplast genome including ORFs and genetic code; (3) identified SSR, tandem repeats and forward repeats of the genome; (4) carried out a phylogenetic analysis of the 68 chloroplast genomes based on 24 conserved genes; (5) compared the chloroplast genome rearrangement of 10 species; (6) analyzed the synteny of U. flexuosa and 12 other species in Chlorophyte; and (7) comprehensively compared the chloroplast genome homology of four Ulva species
We found that organellar genomes in other species across Ulvophyceae were high rearranged comparing with U. flexuosa, while those among Ulva spp. were high conserved
Summary
The macroalgae representing the cosmopolitan green algae Ulva flexuosa Wulfen species have been found in Europe since the mid-1800s [1], which are very common and regularly encountered in fresh waters, slightly saline waters, and estuaries [2], containing the characteristics of transitional species. As one of the original species in green tide outbreak in Yellow Sea of China since 2008, U. flexuosa has attracted global attention for its fast growth if given appropriate nutrient supply, with maximum growth rate of 73% d-1 at room temperature under light intensity of 70 μmolÁm-2Ás -1 [3]. U. flexuosa belongs to Ulvophyceae, with thalli composed of uninucleate cells, and is difficult to be set apart from species among Ulva spp., since the latter is often sheet like in external morphology [5]. The rRNA ITS region, 5S and partial rbcL gene
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