What is the origin of the glycosome?
Where exactly did the plant-like
enzymes come from?
Here, we attempt to explain
the how and why of trypanosomes'
unique metabolic characteristics.
Evolutionary theories are paired with
biological observations
and species survival tactics!
Keep reading!
It's just getting good!
Evolutionary
Mechanisms:
Proposing Glycosome Explanations
Evolution
is often associated only with Darwin's experiments...
3
but
the passage of time has an effect on all creatures!
Welcome to Trypanosome Evolution!
Overview: Trypanosomatids bear a considerable number of plant-like enzymes, many more above the scope of the topics discussed today!
Some of the enzymes are related to chloroplast homologs and
some are related to plant cytosol homologs.
Please read on to trace an explanation of trypanosome's aquisition of a glycosome!
To better understand the evolutionary mechanisms and relationships, read the short
overview and then follow the numbered steps with the
corresponding images on the diagram.
Tracing Evolutionary History
1. Primary Endosymbiosis
A long, long time ago a protozoon consisted of a nucleus, a mitochondrion, and a peroxisome. It feeds on an ancient cyanobacterium that contains only a plastid.
This step is called primary endosymbiosis and follows a "You are what you eat." mentality.
2. Meal Plastid DNA to Predator Nucleus
Next, a green alga like organism is created as cyanobacterial genes leave the plastid and enter the protozoon's nucleus. When organelles such as the plastid lyse inside a host cell, a whole genome's worth of DNA from the cyanobacterium is in the cytosol and just waiting to get into the nuclear chromosome of the protozoon (Martin and Borst, 766).
3. Secondary Endosymbiosis
The process has the potential to stop there. The green alga may live a very peaceful and coexistent life with flagellates. But the flagellates get hungry and devour green alga in a process of secondary endosymbiosis. The secondary refers only that a similar action had happened before in the organism's evolutionary history.
4. Secondary Gene Transfer
The important features here are the acquisition of a plastid as well as the transfer of cyanobacterial genes from the plastid to the nucleus of the alga and MORE IMPORTANTLY to the nucleus of the HOST!
5. A Division in Speciation
The event here takes place that divides the orders of Euglenida and Kinoplastida. The red arrow indicates the branching point for Kinoplastida and consequently trypanosomes. The higher path leads to the evolution of Euglenida and the lower path to Kinoplastida.
6. Species as We Know Them Today
The Euglenoids possess a nucleus that houses many plant-like enzymes originating from primary and secondary endosymbiosis, peroxisomes that acquired many metabolic enzymes, and an intact plastid remnant of the algal predecessor.
Making Evolutionary History
Schematic
diagram indicating how trypanosomes may have come to acquire their
plant-like genes. The common ancestry indicated here for the euglenid
and trypanosome plastid is the simplest of several possibilities to
account for the current findings.
Conclusions
The Kinoplastids possess also a nucleus with enzymes of plant-like origin.
However, in addition to the enzymes that Euglenoids have, Kinoplastida in addition
has gained all of the material of the plastid, and have lost it sometime in their evolutionary history. The proteins that were once inside of the plastid have been redirected to specialized organelles called glycosomes, completely original to Kinoplastida.
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