MSUToday
Published: Jan. 31, 2018

MSU research on photosynthesis could transform how the process is studied

By: Allyson Hamzey Media Communications ally.hamzey@cabs.msu.eduContact(s): Igor Houwat MSU-DOE Plant Research Laboratory office: (517) 353-2223 houwatig@msu.edu

Michigan State University scientists have discovered a significant role that a particular protein complex plays in the process of photosynthesis, potentially changing how scientists study the process entirely.

In a new study published in the journal Photosynthesis Research, scientists at the MSU Department of Energy Plant Research Laboratory found how, Photosystem I -- or PSI, a protein complex -- protects plants from excessive sunlight exposure and helps navigate plants through old age.

“Our study suggests that some basic photosynthesis mechanisms may have been misunderstood and that PSI may do more things, play more central roles, than was previously recognized,” said Eliezer Schwarz, co-author on the study.

The basics of photosynthesis, or the process that converts sunlight into food and energy to power life on earth, is now common knowledge. But the details of its inner workings remain mysterious to scientists.

Take this number: Plants store about one percent of the sunlight they absorb as biomass suitable for human use. The rest is shed, partially in response to environmental stresses like excessive light exposure or drought conditions.

Researchers think that bumping up that storage rate, even by a small percentage -- one or two percent -- could dramatically increase crop yields. Until it is fully understood how photosynthesis adapts to changes in the environment, that goal remains elusive.

“PSI, one of the fundamental photosynthetic protein complexes, has generally been regarded as more stable and less involved in responding to changes in the environment that affect photosynthetic productivity,” said Schwarz, co-author on the study.

But Schwarz, alongside co-authors Stephanie Tietz and John Froehlich, now thinks otherwise.

PSI works with another protein complex called PSII. Both host icon light-harvesting antennae that capture sunlight, a bit like how a car antenna captures radio waves. The antennae usually stick around their respective complexes, but some will hop around.

“PSII can have different amounts of an antenna protein complex, called LHCII -- it’s the one that makes plants look green,” Schwarz said. "In some cases, a small fraction of LHCII can leave PSII and associate with PSI. This has been understood as one of the ways a plant calibrates its light absorption, balancing the amount of energy absorbed by each photosystem.”

The researchers report unusually massive amounts of LHCII migration to PSI when:

  • There is excessive sunlight that could potentially damage PSII complexes. As a consequence, they release their light-harvesting antennae to lower light absorption rates. PSI “stores” these antennae as a safety net.
  • Plants age and start degrading various cellular proteins, including PSII. This leads to free-floating antennae that could significantly harm the plant cell if left alone. In response, PSI picks the antennas up to prevent any damage. 

According to Schwarz, PSII has traditionally been the focus of research, specifically when it comes to light stress responses.

“Our study suggests that some basic photosynthesis mechanisms may have been misunderstood and that PSI may do more things, play more central roles, than was previously recognized,” said Schwarz.