Researchers show molecular structures involved in plant respiration

All plants and animals thrive, energy free 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 these differences can help an agricultural revolutionary.

“Plant respiration is a crucial biological process 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. “When you think of crops, the extent to which they grow is related to biomass accumulation and the interaction between photosynthesis and respiration.”

In a study appears in eLife, Maldonado, Letts and colleagues provide the oldest, atom-level, 3-D structure of the largest protein complex (complex I) involved in the plant mitochondrial electron transport chain.

“For mammals like yeast, we have higher resolution structures of the whole electron transport chain and even supercomplexes, which are complexes of complexes, but for plants it has been a very black box,” Maldonado said. “To this day.”

Inventing the structure and functionality of these plant protein complexes can help researchers improve agriculture and even design better pesticides.

“Many pesticides actually target the mitochondrial electron transport chain complexes of the plague,” Letts said. “So by understanding the structures of the plant’s complexes, we can also design better targeted pesticides or fungicides that kill the fungus but not the plant and not the person eating the plant. . “

Mung beans grow in the dark

To make their food, plants use chloroplasts to perform photosynthesis. But chloroplasts may pose a problem for 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,” Maldonado said.

These similarities make it difficult to isolate mitochondria from chloroplasts in a lab environment. To circumvent this, the researchers used “etiolated” mung beans (Vigna radiata), which means that they grew the plants in the dark, which prevented chloroplasts from developing and causing the plants to appear pale.

“Mung beans are an oilseed, so they store energy in the form of seed oils and then the sprouts start to burn those oils like its fuel,” Letts said. Without chloroplasts, the plants cannot photosynthesize, limiting their energy flows.

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

“We used single-particle cryoelectron microscopy to resolve the structure of the complexes after purifying mitochondrial samples,” Letts said.

With these structures, scientists can see, at the atomic level, how the building block proteins of complex I are composed and how those structures and their composition differ compared to the complexes present in the cells of mammals, yeasts and bacteria.

“Our structure shows us for the first time the details of a complex I-module that is unique to plants,” the researchers said. “Our experiments also gave us hints that this compounding agent may not only be a step towards the fully assembled complex I, but may have a separate function of its own.”

The researchers speculated that the unique modular structure of complex I plants could give them the flexibility to thrive as sessile organisms.

“Unlike us, plants are in the ground, so they need to be adapted,” Letts said. “When something changes, they can not just get up and go as we can, so they have evolved to be extremely flexible in their metabolism.”

With the structure of complex I now in hand, the researchers plan to perform functional experiments. More understanding of functionality of complex I can open the door to making crops more energy efficient.