Underwater 'breathing' plants could be key to stress-resistant crops
Researchers examine the formation of air channels in wetland plants, a protective trait that makes them resilient to environmental stresses

Date:
February 6, 2022
Source:
Nagoya University
Summary:
Wetland plants have a high tolerance against flooding due to
the formation of 'lysigenous aerenchyma,' air channels that help
transfer gases to the submerged roots. These channels also help the
plant withstand drought and nutrient deficiency. Now, scientists
investigate the underlying mechanism of aerenchyma formation to
understand the phenomenon better, opening doors to the development
of crops that are resilient against extreme weather changes.



FULL STORY ========================================================================== Wetland plants have a high tolerance against flooding due to the formation
of "lysigenous aerenchyma," air channels that help transfer gases to the submerged roots. These channels also help the plant withstand drought and nutrient deficiency. Now, scientists from Japan investigate the underlying mechanism of aerenchyma formation to understand the phenomenon better,
opening doors to the development of crops that are resilient against
extreme weather changes.


========================================================================== Floods and droughts are the main environmental disasters responsible
for most crop failures. Aerenchyma formation can help crops cope with
these environmental stresses. However, it is not commonly observed in non-wetland species like wheat and maize, which are staple food crops
in certain areas of the world. Researchers Takaki Yamauchi and Mikio
Nakazono from Nagoya University, Japan, have surveyed literature on
the topic to get a concrete overview of the various factors involved
in aerenchyma formation. "If we can genetically control the timing and
amount of lysigenous aerenchyma formation in roots of all agronomically important crops, such as maize, wheat and soybean, the global crop
production loss could be dramatically reduced," says Dr.

Nakazono.

Dr. Yamauchi and Dr. Nakazono suggest imagining the lysigenous aerenchyma
to a snorkel used to breathe underwater. During flooding, the roots
get cut off from oxygen and other vital gases needed for survival. In
response, the plant creates air pathways connecting the submerged
regions of the plant to the parts above water. Similar to a snorkel,
these pathways help the plant "breathe" by transporting gases to the
submerged roots. Moreover, the air channels reduce the energy requirement
for the breathing process and can help the plant conserve energy during
extreme conditions of drought or nutrient deficit.

The researchers found that a phytohormone called "auxin" is required for
the formation of aerenchyma during normal root growth, and identified two factors leading to the induction of aerenchyma formation in response to flooding. The phenomenon begins when the roots are submerged underwater
in aerobic conditions. The restrictions to gas exchange cause ethylene
to accumulate in the roots, which encourage the production of respiratory
burst oxidase homolog (RBOH) -- an enzyme responsible for reactive oxygen species (ROS) production.

As it turns out, the released ROS triggers cell death in the tissues,
forming cavities for the passage of gases.

The RBOH can also be activated by the presence of calcium (Ca2+) ions
that are transported from the apoplast (water pathways). Certain plants
have calcium- dependent protein kinases that use Ca2+ to add phosphates
to the RBOH, stimulating it to produce ROS. This effect occurs at later
stages as the plants gradually experience oxygen-deficient conditions
after prolonged underwater submersion.

While aerenchyma is mostly associated with plants that have adapted
to soils with high water content, it can also develop in upland
plants under drought and nutrient deficiency. Low concentrations
of nitrogen and phosphorus, essential nutrients required for plant
growth, was found to increase the ethylene sensitivity, stimulating the formation of aerenchyma. Moreover, ethylene was also a common factor
in triggering aerenchyma in maize, offering a way to improve the crop's resilience. "The increase in ethylene sensitivity could be an effective strategy to stimulate aerenchyma formation in the absence of restricted
gas diffusion," speculates Dr. Yamauchi.

While the mechanism behind aerenchyma formation remains uncertain,
suggesting the need for further research, the findings of this study
open up the possibility of improving crop resilience and paving the way
for better food security in the wake of climate change.

The new paper has been based on the following two papers: "Fine control of aerenchyma and lateral root development through AUX/IAA- and ARF-dependent auxin signaling." Proceedings of the National Academy of Sciences of the
United States of America, 116, 2019, DOI: 10.1073/pnas.1907181116 "An
NADPH oxidase RBOH functions in rice roots during lysigenous aerenchyma formation under oxygen-deficient conditions." The Plant Cell, 29, 2017,
DOI: 10.1105/tpc.16.00976 Funding Information: This study was supported
by the Japan Science and Technology Agency PRESTO grants JPMJPR17Q8
to T.Y. and Grant-in-Aid for Transformative Research Areas (A) (MEXT
KAKENHI grant JP20H05912) to M.N.

========================================================================== Story Source: Materials provided by Nagoya_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Takaki Yamauchi, Mikio Nakazono. Mechanisms of lysigenous aerenchyma
formation under abiotic stress. Trends in Plant Science, 2022; 27
(1): 13 DOI: 10.1016/j.tplants.2021.10.012 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220206154432.htm
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