Autophagy: The unlikely hero that balances zinc and iron in plants
Researchers highlight a novel function of autophagy in restoring zinc and
iron balance in plants under nutrient stress conditions

Date:
August 18, 2021
Source:
Meiji University
Summary:
Nutrient imbalances can adversely impact crop health and
agricultural productivity. The trace elements zinc and iron are
taken up by the same 'transporters' in plants; so, zinc deficiency
can result in excess uptake of iron. How does the plant cope with
this imbalance? Researchers reveal that autophagy, the process
of intracellular self-degradation, may have an unexpected role in
restoring zinc-iron balance in plants.



FULL STORY ========================================================================== Nutrient imbalances can adversely impact crop health and agricultural productivity. The trace elements zinc and iron are taken up by the
same "transporters" in plants; so, zinc deficiency can result in excess
uptake of iron. How does the plant cope with this imbalance? Researchers
from Meiji University, Japan, reveal that autophagy, the process of intracellular self- degradation, may have an unexpected role in restoring zinc-iron balance in plants.


==========================================================================
A balance of nutrients and minerals in the soil is essential for
the optimal growth of plants. A deficiency or surplus of specific
nutrients can have detrimental effects on the growth and health of
plants, thus affecting the overall quality and quantity of agricultural produce. Nutrient imbalances have become increasingly prevalent, given
the excessive heavy metal contamination from industrial activities.

Zinc, an essential trace element, is important for a number of important
life processes. Interestingly, the uptake and transport of zinc and iron, another essential nutrient, is facilitated through a common group of
proteins known as "zinc- and iron-regulated transporter-like proteins
(ZIPs)." This means that a disturbance in this zinc-iron "seesaw" can
thus lead to symptoms induced by their respective deficiencies. That is,
if a soil doesn't have enough zinc, the ZIPs cope by increasing their
uptake of iron, resulting in an increase in reactive oxidative species
and chlorosis (yellowing of leaves). Conversely, an excess of zinc leads
to decreased uptake of iron. How is the intra-cellular balance of these nutrients restored in such situations? Probing deeper into the likely mechanisms of zinc-iron balance or "homeostasis," researchers from Meiji University, Japan, explored the potential role of autophagy, a process of self-degradation and recycling, in restoring zinc-iron balance in plant
cells. Describing their study published in Trends in Plant Science, corresponding author and Professor, Dr. Kohki Yoshimoto says, "While
most studies have addressed the role of nutrient uptake and transport,
we propose a novel model on how autophagy supplies mobile zinc and iron
ions under zinc starvation- and zinc excess-stress, respectively; thus, balancing the intracellular zinc-iron seesaw to adapt to a wide range
of environmental zinc concentrations." Autophagy has been previously
shown to increase the availability of zinc in plant systems. In
Arabidopsis, a plant model system, "atg" mutants, which are deficient
in autophagy responses, have lowered levels of zinc and exhibit severe chlorosis. Moreover, zinc deficiency is known to trigger autophagy,
which resupplies mobile zinc ions for plant growth. In autophagy deficient mutants, however, this activation in impaired, leading to classic symptoms
of zinc deficiency.

Excess zinc is also toxic to plants, and autophagy is the savior in
such cases too. Plants exhibit iron deficiency symptoms in zinc excess conditions.

Autophagy is activated under zinc excess conditions to resupply mobile
iron ions from non-mobile forms such as iron bound proteins. Autophagy
improves the bioavailability of iron and suppresses the iron deficiency symptoms.

Moving on from the role of autophagy in zinc-iron homeostasis, researchers proceeded to elucidate nutrient sensing mechanisms responsible
for activating autophagy. Transcription factors bZIP19 and bZIP23,
belonging to the basic leucine zipper family, detect changes in the
levels of intracellular zinc and accordingly regulate the expression
of transporter proteins on the cell membrane. The researchers speculate
that these proteins may be the regulators that switch autophagy response
"on" or "off" depending on the status of zinc. A similar mechanism may
also come into play in conditions of iron deficiency with excess zinc,
to restore iron levels.

Overall, autophagy functions as a feedback mechanism that can react to deficiency or excess zinc induced stress, and accordingly alter the bio- available fraction of nutrients in plant cells.

Concluding with the long-term applications of their findings,
Dr. Yoshimoto remarks, "Our model provides a new perspective to metal homeostasis in plants.

This can contribute to the development of new cultivation techniques
and robust crop varieties that are resistant to nutrient level
fluctuations. Furthermore, our findings may also be applied to human
health to resolve zinc deficiency- induced symptoms, a major problem
in developing countries." Autophagy, known for its quintessential
degradative role, may just turn out to be the hero for plant health! ========================================================================== Story Source: Materials provided by Meiji_University. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Daiki Shinozaki, Kohki Yoshimoto. Autophagy balances the zinc-iron
seesaw
caused by Zn-stress. Trends in Plant Science, 2021; 26 (9): 882
DOI: 10.1016/j.tplants.2021.06.014 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210818083951.htm

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