The crisis management system of plants responding to environmental changes
Department of Life and Environmental Sciences,
Graduate School of Arts and Sciences, The University of Tokyo
Professor Yuichiro Watanabe[About my research]
In recent years, Japan has been hit by frequent heat waves, heavy rains, typhoons, andearthquakes, and various natural disasters have occurred throughout the Japanesearchipelago. I express my deepest sympathies to all those affected. Different
infrastructures and houses were severely damaged, and so did fields, forests, and coastal
areas, which support daily human life.

Figure 1 Nazuna plant (Capsella bursa-pastoris) growing
in Rikuzentakata City one year after the Great East JapanEarthquake.

I found a plant under my feet (Photo 1) when I visited the disaster site. When we lookat each of the plants around us, they seem very weak. Come to think of it, it has been 450
million years since plants first appeared on land. During that time, plants have continued
to survive even in the face of significant climate changes that caused the extinction ofdinosaurs and other animals. Plants have differentiated and adapted to various climates.
Plants came to live on land and extant ones have survived up to our age by securing waterand competing with significant temperature changes. And they have been provided foodfor animals and us humans.
Our studies have been conducted on how plants on how development proceeds byregulating expression of various genes. Also, we have conducted studies of how plants switch
genes on and off in response to different environmental changes. When we grow plants byour hands, we try to protect them somehow so that they can grow peacefully. In fact, plants
are not fragile; when environmental changes occur in wild nature, plants do not immediately
die but instead respond in some way on their own to survive.

When the growing

environment becomes unfavorable during development or growth, plants often change theirgene expression patterns. For example, it is well known that young plants that have sprouted
in the shade of other plants will try to get to the sun early and accelerate stem elongation. I
am interested in these potential adaptability by modulating gene expression patterns in plants.
I would like to know the as yet unknown gene expression patterns that plants have for crisis
management. Such knowledge must be meaningful for sustainable agriculture and forestry
and for learning the key to instructing organisms and humans how to live in the global
environmental changes that may occur.
When plants are exposed to higher-than-normal temperatures, they exhibit different
gene expression patterns than they did before. I am interested in the meaning of such new
expression patterns against the tolerance to high temperatures (biological meaning forsurvival) and how they dynamically change their gene expression patterns (crisis management
system for survival). Plants generally have about 25,000 ~ 50,000 protein-coding genes.
Exposure to high temperatures can cause to increase of over a thousand genes’ expression
with simultaneous decrease of nearly the same number of genes’ expression. This cannot be
explained by the increased transcription initiation alone, which increases expression. It isalso necessary to suppress the expression of genes that were expressed before theenvironmental change and are "no longer useful" or that have "low priority" in an emergency.
In other words, plants have mechanisms to turn on the expression of genes that areappropriate for the purpose and to turn off the expression of genes that are not appropriate
for the purpose. In this context, I am focusing on the degradation mechanism of specificgene mRNA (Figures 2 and 3) to suppress protein translation from specific gene mRNA.

Figure 2 P-body which degrades specific mRNAs. The
structure is commonly found in the cytoplasm of eukaryoticorganisms; its function is essential for growth and survival.

Figure 3 Stress granule (SG) which suppresses the translation from specific mRNAs. The
structure is commonly found in the cytoplasm of eukaryotes, and their function is essential
for growth by providing emergency refuge for specific mRNAs so that the mRNAs become
available again when the crisis passes.
I also have been investigating the mechanism of repression of specific mRNAs by
microRNAs, which are non-coding RNAs as short as 19-24 nucleotides in length.

Tounderstand the system, I started my research with Arabidopsis thaliana (Fig. 4).

Figure 4 Arabidopsis (35S:miR156), whichconstantly expresses a microRNA called miR156,does not flower easily compared to that wild-type(WT).

And now, I have expanded the study to include liverwort (Marchantia polymorpha),
phylogenetically located at the base of land plants. Various studies have shown that land
plants all have, without exception, standby genes for responding to environmental changes,
protein genes involved in the regulatory mechanism of expression, or crisis management
mechanisms, as introduced here. I am trying to understand the regulatory expression system
related to such crisis management. Through this research, I would like to clarify the essential
strategies of the terrestrial plants and build up various ways to make coexistence of humanbeings and botanical world.