Fig. 7
Schematic representation of the probable basis of polyphyletic origin of the MEP-pathway genes. The three proposed scenarios supporting polyphyletic origin of the MEP-pathway genes are: (I) Horizontal Gene Transfer (HGT) of the MEP-pathway genes from chlamydial (magenta) to cyanobacteria (cyan) pangenome followed by the cyanobacterial Endosymbiotic Gene Transfer (EGT) to the eukaryotic host; (II) HGT of genes from Chlamydiae-to-ancestral eukaryotes; (III) Co-contribution of cyanobacteria and Chlamydiae to the MEP-pathway genes. In all the probable cases, the events were ensued by the transfer of genetic material from the endosymbiont(s) to the host nuclear genome (white circle). The estimated average of global temperature (Tm) fluctuation and atmospheric oxygen (O2) are modified based on Harada, et al., 2015, Fiorella and Sheldon 2017, and Zhang et al., 2018. The authors depict the image by themselves