Study finds missing link in the evolutionary history of carbon-fixing
protein Rubisco

Date:
August 31, 2020
Source:
University of California - Davis
Summary:
A team has discovered a missing link in the evolution of
photosynthesis and carbon fixation. Dating back more than 2.4
billion years, a newly discovered form of the plant enzyme rubisco
could give new insight into plant evolution and breeding.



FULL STORY ==========================================================================
A team led by researchers at the University of California, Davis, has discovered a missing link in the evolution of photosynthesis and carbon fixation. Dating back more than 2.4 billion years, a newly discovered
form of the plant enzyme rubisco could give new insight into plant
evolution and breeding.


========================================================================== Rubisco is the most abundant enzyme on the planet. Present in plants, cyanobacteria (also known as blue-green algae) and other photosynthetic organisms, it's central to the process of carbon fixation and is one of
Earth's oldest carbon-fixing enzymes.

"It's the primary driver for producing food, so it can take CO2 from the atmosphere and fix that into sugar for plants and other photosynthetic organisms to use. It's the primary driving enzyme for feeding carbon
into life that way," said Doug Banda, a postdoctoral scholar in the lab
of Patrick Shih, assistant professor of plant biology in the UC Davis
College of Biological Sciences.

Form I rubisco evolved over 2.4 billion years ago before the Great
Oxygenation Event, when cyanobacteria transformed the Earth's atmosphere
by producing oxygen through photosynthesis. Rubisco's ties to this ancient event make it important to scientists studying the evolution of life.

In a study appearing Aug. 31 in Nature Plants, Banda and researchers
from UC Davis, UC Berkeley and the Lawrence Berkeley National Laboratory
report the discovery of a previously unknown relative of form I rubisco,
one that they suspect diverged from form I rubisco prior to the evolution
of cyanobacteria.

The new version, called form I-prime rubisco, was found through genome sequencing of environmental samples and synthesized in the lab. Form
I-prime rubisco gives researchers new insights into the structural
evolution of form I rubisco, potentially providing clues as to how this
enzyme changed the planet.



==========================================================================
An invisible world Form I rubisco is responsible for the vast majority
of carbon fixation on Earth. But other forms of rubisco exist in bacteria
and in the group of microorganisms called Archaea. These rubisco variants
come in different shapes and sizes, and even lack small subunits. Yet
they still function.

"Something intrinsic to understanding how form I rubisco evolved is
knowing how the small subunit evolved," said Shih. "It's the only form
of rubisco, that we know of, that makes this kind of octameric assembly
of large subunits." Study co-author Professor Jill Banfield, of UC
Berkeley's earth and planetary sciences department, uncovered the new
rubisco variant after performing metagenomic analyses on groundwater
samples. Metagenomic analyses allow researchers to examine genes and
genetic sequences from the environment without culturing microorganisms.

"We know almost nothing about what sort of microbial life exists in
the world around us, and so the vast majority of diversity has been
invisible," said Banfield. "The sequences that we handed to Patrick's lab actually come from organisms that were not represented in any databases."
Banda and Shih successfully expressed form I-prime rubisco in the lab
using E.

coli and studied its molecular structure.



==========================================================================
Form I rubisco is built from eight core large molecular subunits with
eight small subunits perched on top and bottom. Each piece of the
structure is important to photosynthesis and carbon fixation. Like
form I rubisco, form I- prime rubisco is built from eight large
subunits. However, it does not possess the small subunits previously
thought essential.

"The discovery of an octameric rubisco that forms without small subunits
allows us to ask evolutionary questions about what life would've
looked like without the functionality imparted by small subunits,"
said Banda. "Specifically, we found that form I-prime enzymes had to
evolve fortified interactions in the absence of small subunits, which
enabled structural stability in a time when Earth's atmosphere was rapidly changing." According to the researchers, form I-prime rubisco represents
a missing link in evolutionary history. Since form I rubisco converts
inorganic carbon into plant biomass, further research on its structure
and functionality could lead to innovations in agriculture production.

"Although there is significant interest in engineering a 'better'
rubisco, there has been little success over decades of research," said
Shih. "Thus, understanding how the enzyme has evolved over billions of
years may provide key insight into future engineering efforts, which
could ultimately improve photosynthetic productivity in crops."

========================================================================== Story Source: Materials provided by
University_of_California_-_Davis. Original written by Greg Watry. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Douglas M. Banda, Jose H. Pereira, Albert K. Liu, Douglas J. Orr,
Michal
Hammel, Christine He, Martin A. J. Parry, Elizabete Carmo-Silva,
Paul D.

Adams, Jillian F. Banfield, Patrick M. Shih. Novel bacterial
clade reveals origin of form I Rubisco. Nature Plants, 2020; DOI:
10.1038/ s41477-020-00762-4 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200831131632.htm

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