Research identifies proteins that support photosynthesis in iron
deficient plants
New study sheds light on genetic processes for plant protection

Date:
October 12, 2021
Source:
Dartmouth College
Summary:
As climate change poses risks to plant growth and food supply,
researchers have identified how iron deficient plants optimize
photosynthesis and regulate light protection.



FULL STORY ========================================================================== Researchers have identified how iron deficient plants protect themselves
from damaging light, according to a Dartmouth study.


==========================================================================
The study, published in Proceedings of the National Academy of Sciences,
shows how plants lacking iron optimize photosynthesis, and it describes
the genetic processes that regulate light protection in plants that lack sufficient levels of the mineral.

"We are trying to identify the downstream genes that control the
efficiency of sunlight capture and conversion in plants," said Mary
Lou Guerinot, professor of biological sciences at Dartmouth and senior researcher of the study. "This study adds to what we know about how
plants respond to environmental change at a critical time for our human
food supply." Iron is important in humans for oxygen transport in the
blood and is a key cofactor for many enzymatic reactions including energy generation in mitochondria. According to research cited in the study,
iron deficiency is the most prevalent nutritional disorder in humans.

Iron is also an important nutrient for plants. Iron deficiency severely
limits photosynthesis, leading to decreased yields.

Since most people obtain the majority of their calories and nutrients
from plants, it is important that researchers understand how plants
process the mineral.



========================================================================== "Iron deficiency has many adverse effects on photosynthesis," said
Guerinot.

"It is critical that plants get sufficient levels of iron while also
adjusting metabolism to compensate for reduced iron availability and
reduced photosynthetic efficiency." According to the paper, the iron
uptake system in plants is regulated by a cascade of activities, many
of which have been discovered by Dartmouth's Guerinot Lab. During iron deficiency, plants alter the expression of genes to increase iron uptake, distribution, and utilization.

While much is known about the response to iron deficiency in plant roots, little is known about the regulation of the iron deficiency response
in leaves.

The research focuses on "photosystem II," the protein complex that
performs the water-splitting process of photosynthesis that allows light
energy to be converted into chemical energy in the leaves. According to
the paper, photosystem II is a major target of damage to chloroplasts
in iron deficient leaves. Chloroplasts -- where energy-producing
photosynthesis takes place in a plant -- store 90% of the iron in
plant leaves.

"Many strategies to optimize iron usage have been documented, but we knew fairly little about the mechanisms of how chloroplasts adapt to iron
deficiency prior to this study," said Garo Akmakjian, a PhD student at Dartmouth when the work was carried out and lead author of the paper.



==========================================================================
The research team narrowed their investigation by following the cause of
light- induced leaf bleaching that was observed during iron deficiency
in a mutant that failed to make the regulatory protein ILR3. Bleaching
is commonly observed during "high-light stress" in plants and gave the researchers a clue that these mutant plants were now more sensitive
to light.

The study shows that the regulatory proteins ILR3 and PYE protect plants
from absorbing too much light during iron deficiency. Changes in the
internal structure of chloroplasts under the control of these proteins
allow for repair of photosystem II, preventing the production of harmful reactive oxygen species.

"We found that excess light can cause leaves to bleach and die during
iron deficiency, but ILR3 and PYE's activity prevents the light from
becoming toxic, allowing photosynthesis to occur without the associated
tissue damage in iron- starved plants," said Akmakjian, now a postdoctoral researcher at the University of California, Riverside.

The research team hopes that understanding how plants adapt their photosynthetic machinery during iron deficiency may allow researchers
to optimize plant growth in soils where iron is not bioavailable.

"With climate change, where and how we grow crops is changing," said
Guerinot.

"In the future, we won't have the luxury of only growing crops
in fertile soils rich in nutrients and with plenty of water."
Nabila Riaz, a graduate student at Dartmouth, coauthored the study and
provided Synchrotron X-ray Fluorescence Spectrometry images using X-ray Fluorescence Microprobe (XFM) beamline 4-BM of the National Synchrotron
Light Source II.

========================================================================== Story Source: Materials provided by Dartmouth_College. Original written
by David Hirsch.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Garo Z. Akmakjian, Nabila Riaz, Mary Lou Guerinot. Photoprotection
during
iron deficiency is mediated by the bHLH transcription factors PYE
and ILR3. Proceedings of the National Academy of Sciences, 2021;
118 (40): e2024918118 DOI: 10.1073/pnas.2024918118 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211012102709.htm

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