Schematic of Cyanophora paradoxa. Credit: Courtesy of Bhattacharya Lab |
Atmospheric
oxygen really took off on our planet about 2.4 billion years ago during
the Great Oxygenation Event. At this key juncture of our planet’s
evolution, species had either to learn to cope with this poison that was
produced by photosynthesizing cyanobacteria or they went extinct. It
now seems strange to think that the gas that sustains much of modern
life had such a distasteful beginning.
So
how and when did the ability to produce oxygen by harnessing sunlight
enter the eukaryotic domain, that includes humans, plants, and most
recognizable, multicellular life forms? One of the fundamental steps in
the evolution of our planet was the development of photosynthesis in
eukaryotes through the process of endosymbiosis.
This
crucial step forward occurred about 1.6 billion years ago when a
single-celled protist captured and retained a formerly free-living
cyanobacterium. This process, termed primary endosymbiosis, gave rise to
the plastid, which is the specialized compartment where photosynthesis
takes place in cells. Endosymbiosis is now a well substantiated theory
that explains how cells gained their great complexity and was made
famous most recently by the work of the late biologist Lynn Margulis,
best known for her theory on the origin of eukaryotic organelles.
In a paper “Cyanophora paradoxa genome elucidates origin of photosynthesis in algae and plants” that appeared this week in the journal Science,
an international team led by evolutionary biologist and Rutgers
University professor Debashish Bhattacharya has shed light on the early
events leading to photosynthesis, the result of the sequencing of 70
million base pair nuclear genome of the one-celled alga Cyanophora.
In the world of plants, “Cyanophora
is the equivalent to the lung fish, in that it maintains some primitive
characteristics that make it an ideal candidate for genome sequencing,”
said Bhattacharya.
Bhattacharya
and colleagues consider this study “the final piece of the puzzle to
understand the origin of photosynthesis in eukaryotes.” Basic
understanding of much of the subsequent evolution of eukaryotes,
including the rise of plants and animals, is emerging from the
sequencing of the Cyanophora paradoxa genome, a function-rich species that retains much of the ancestral gene diversity shared by algae and plants.
For
those unfamiliar with algae, they include the ubiquitious diatoms that
are some of the most prodigious primary producers on our planet,
accounting for up to 40% of the annual fixed carbon in the marine
environment.
Bhattacharya
leads the Rutgers Genome Cooperative that has spread the use of genome
methods among university faculty. Using data generated by the Illumina
Genome Analyzer IIx in his lab, Bhattacharya, his lab members Dana C.
Price, Cheong Xin Chan, Jeferson Gross, Divino Rajah and collaborators
from the U.S., Europe and Canada provided conclusive evidence that all
plastids trace their origin to a single primary endosymbiosis.
Now
that the blueprint of eukaryotic photosynthesis has come more clearly
in sight, researchers will be able to figure out not only what unites
all algae as plants but also what key features make them different from
each other and the genes underlying these functions.
Cyanophora paradoxa genome elucidates origin of photosynthesis in algae and plants
