Researchers reveal molecular structures involved in plant respiration


Date:
August 25, 2020
Source:
University of California - Davis
Summary:
New research provides the first-ever, atomic-level, 3D structure
of the largest protein complex (complex I) involved in the plant
mitochondrial electron transport chain. The results could unlock
new advances in agriculture.



FULL STORY ==========================================================================
All plants and animals respire, releasing energy from food. At the
cellular level, this process occurs in the mitochondria. But there
are differences at the molecular level between how plants and animals
extract energy from food sources. Discovering those differences could
help revolutionize agriculture.


========================================================================== "Plant respiration is a crucial process biologically for growth, for
biomass accumulation," said Maria Maldonado, a postdoctoral researcher
in the lab of James Letts, assistant professor in the Department of
Molecular and Cellular Biology, College of Biological Sciences. "If you're thinking of crops, the extent to which they grow is related to biomass accumulation and the interplay between photosynthesis and respiration."
In a study appearing in eLife, Maldonado, Letts and colleagues provide
the first-ever, atomic-level, 3D structure of the largest protein complex (complex I) involved in the plant mitochondrial electron transport chain.

"For mammals or yeast, we have higher resolution structures of the entire electron transport chain and even supercomplexes, which are complexes of complexes, but for plants, it's been an entire black box," said Maldonado.

"Until today." Figuring out the structure and functionality of these
plant protein complexes could help researchers improve agriculture and
even design better pesticides.

"Lots of pesticides actually target the mitochondrial electron transport
chain complexes of the pest," said Letts. "So by understanding the
structures of the plant's complexes, we can also design better-targeted pesticides or fungicides that will kill the fungus but not the plant
and not the human who eats the plant." Growing mung beans in the dark


==========================================================================
To make their food, plants utilize chloroplasts to conduct
photosynthesis. But chloroplasts can pose a problem to scientists studying
the molecular minutiae of the mitochondrial electron transport chain.

"Plants have mitochondria and they also have chloroplasts, which make
the plant green, but the organelles are very similar in size and have
very similar physical properties," said Maldonado.

These similarities make it difficult to isolate mitochondria from
chloroplasts in a lab setting. To get around this, the researchers used "etiolated" mung beans (Vigna radiata), meaning they grew the plants in
the dark, which prevented chloroplasts from developing and caused the
plants to appear bleached.

"Mung beans are an oilseed such that they store energy in the form of
seed oils and then the sprouts start burning those oils like its fuel,"
said Letts.

Without chloroplasts the plants are unable to photosynthesize, limiting
their energy streams.

By separating mitochondria from chloroplasts, the researchers gained a
clearer structural image of complex I and its subcomplexes.



==========================================================================
"We used single-particle cryoelectron microscopy to solve the structure
of the complexes after purifying them from mitochondrial samples,"
said Letts.

With these structures, scientists can see, at the atomic level, how
the building block proteins of complex I are assembled and how those
structures and their assembly differs compared to the complexes present
in the cells of mammals, yeast and bacteria.

"Our structure shows us for the first time the details of a complex I
module that is unique to plants," said the researchers. "Our experiments
also gave us hints that this assembly intermediate may not just be a step towards the fully assembled complex I, but may have a separate function
of its own." The researchers speculated that complex I's unique modular structure may give plants the flexibility to thrive as sessile organisms.

"Unlike us, plants are stuck in the ground, so they have to be
adaptable," said Letts. "If something changes, they can't just get up
and walk away like we can, so they've evolved to be extremely flexible
in their metabolism." With the structure of complex I now in hand, the researchers plan to conduct functional experiments. Further understanding complex I's functionality could open the doorway to making crop plants
more energy efficient.


========================================================================== 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. Maria Maldonado, Abhilash Padavannil, Long Zhou, Fei Guo, James
A Letts.

Atomic structure of a mitochondrial complex I intermediate from
vascular plants. eLife, 2020; 9 DOI: 10.7554/eLife.56664 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200825160558.htm

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