The evolutionary history of lysine biosynthesis pathways within eukaryotes

Area of Science:

• Evolutionary Biology
• Molecular Evolution
• Biochemistry

Background:

• Lysine biosynthesis occurs via the diaminopimelate (DAP) and alpha-aminoadipate (AAA) pathways.
• The AAA pathway was considered nearly exclusive to fungi, with the alpha-aminoadipate reductase (AAR) gene in Corallochytrium limacisporum initially thought to be a fungal synapomorphy.

Purpose of the Study:

• To investigate the evolutionary distribution of the AAR gene across eukaryotes.
• To analyze the distribution of the lysA gene, a core component of the DAP pathway.
• To re-evaluate the evolutionary history of lysine biosynthesis pathways and the role of lateral gene transfer (LGT).

Main Methods:

• Conducted a broad bioinformatic search for the AAR gene in various eukaryotic lineages.
• Analyzed the distribution patterns of the lysA gene across different eukaryotic taxa.
• Interpreted gene distribution data in the context of eukaryotic phylogeny and potential LGT events.

Main Results:

• The AAR gene is present in several unicellular opisthokonts, refuting its status as a synapomorphy between fungi and C. limacisporum.
• The AAR gene appears to be exclusive to Excavata and Unikonts.
• The lysA gene is found in diverse, unrelated taxa across major eukaryotic lineages, strongly suggesting multiple lateral gene transfer (LGT) events.

Conclusions:

• The evolutionary history of both AAR and lysA genes is more intricate than previously understood.
• The presence of AAR in non-fungal opisthokonts indicates its broader distribution and challenges prior evolutionary assumptions.
• The widespread distribution of lysA, particularly its acquisition by Monosiga brevicollis and Capsaspora owczarzaki from a proteobacterial ancestor, highlights the significant role of LGT in eukaryotic evolution.