Xing, X.-y. | Search bioRxiv

bioRxiv2020

Chroococcidiorella tianjinensis, gen. et sp. nov. (Trebouxiophyceae, Chlorophyta), a green alga arises from the cyanobacterium TDX16

All algae documented so far are of unknown origin. Here, we provide a taxonomic description of the first origin-known alga TDX16-DE that arises from the Chroococcidiopsis-like endosymbiotic cyanobacterium TDX16 by de novo organelle biogenesis after acquiring its green algal host Haematococcus pluvialiss DNA. TDX16-DE is spherical or oval, with a diameter of 2.0-3.6 {micro}m, containing typical chlorophyte pigments of chlorophyll a, chlorophyll b and lutein and reproducing by autosporulation, whose 18S rRNA gene sequence shows the highest similarity of 99.7% to that of Chlorella vulgaris. However, TDX16-DE is only about half the size of C. vulgaris and structurally similar to C. vulgaris only in having a chloroplast-localized pyrenoid, but differs from C. vulgaris in that (1) it possesses a double-membraned cytoplasmic envelope but lacks endoplasmic reticulum and Golgi apparatus; and (2) its nucleus is enclosed by two sets of envelopes (four unit membranes). Therefore, based on these characters and the cyanobacterial origin, we describe TDX16-DE as a new genus and species, Chroococcidiorella tianjinensis gen. et sp. nov., which sets the basis for multidisciplinary research.

plant biology↗

bioRxiv2017

De novo organelle biogenesis in the cyanobacterium TDX16 released from the green alga Haematococcus pluvialis

It is believed that eukaryotes arise from prokaryotes, which means that organelles can form in the latter. Such events, however, had not been observed previously. Here, we report the biogenesis of organelles in the endosymbiotic cyanobacterium TDX16 that escaped from its senescent/necrotic host cell of green alga Haematococcus pluvialis. In brief, organelle biogenesis in TDX16 initiated with cytoplasm compartmentalization, followed by de-compartmentalization, DNA allocation, and re-compartmentalization, as such two composite organelles-the primitive chloroplast and primitive nucleus sequestering minor and major fractions of cellular DNA respectively were formed. Thereafter, the eukaryotic cytoplasmic matrix was built up from the matrix extruded from the primitive nucleus; mitochondria were assembled in and segregated from the primitive chloroplast, whereby the primitive nucleus and primitive chloroplast matured into nucleus and chloroplast respectively; while most mitochondria turned into double-membraned vacuoles after matrix degradation. Results of pigment analyses, 16S rRNA and genome sequencing revealed that TDX16 is a phycocyanin-containing cyanobacterium resembling Chroococcidiopsis thermalis, which had acquired 9,017,401bp DNAs with 10301 genes form its host. Therefore, organelle biogenesis in TDX16 was achieved by hybridizing the acquired eukaryotic DNAs with its own ones and expressing the hybrid genome.\n\nOrganelle biogenesis in TDX16 results in its transition into a new eukaryotic alga TDX16-DE, which provides a reference to re-understand the development, structure, function and association of organelles in eukaryotes and the reasons behind them, and has implications on other sections of biology, particularly cancer biology and evolutionary biology: (1) the formation and maturation of the small organelle-less nascent cancer cells share striking similarities with TDX16 development and transition, so, it is most likely that cancer cells arise from bacteria; (2) organelle biogenesis in TDX16 uncovers a way of new organelle and new single-celled eukaryote formation, and in light of which, the ancestral organelles were likely formed in rather than transformed form the endosymbiotic prokaryotes that had acquired their hosts DNAs.

cell biology↗