Plant living with only one leaf reveals fundamental genetics of plant
growth
Future possibilities include controlling size of crop leaves

Date:
August 25, 2020
Source:
University of Tokyo
Summary:
Clinging to the walls of tropical caves is a type of plant with
a single leaf that continues to grow larger for as long as the
plant survives.

Researchers hope that their study of this unusual species may
help inspire future genetic tools to control the size of common
crop plants.



FULL STORY ========================================================================== Clinging to the walls of tropical caves is a type of plant with a
single leaf that continues to grow larger for as long as the plant
survives. Researchers at the University of Tokyo hope that their study
of this unusual species may help inspire future genetic tools to control
the size of common crop plants.


==========================================================================
"We are pleased that we finally made a small breakthrough studying this
plant," said Professor Hirokazu Tsukaya, who led the recent research
project.

The plant's scientific name, Monophyllaea glabra, means "hairless species
of one-leaf plant." M. glabra sprouts from a seed with two embryonic
leaves called cotyledons, but only one of the cotyledons continues to
develop into a leaf.

All Monophyllaea species grow one leaf that, as far as scientists have observed, can continue growing bigger as long as the plant lives. Most
plants have no limit on the number of leaves they can grow, but those
leaves do have a predetermined maximum size.

Tsukaya first tried working with Monophyllaea in the early 1990s after
a trip to see the plants growing in their native habitat in Thailand.

"Monophyllaea like to live in limestone caves in Southeast Asia. If you
have a chance to go there, you can see these plants easily," said Tsukaya.



==========================================================================
The same curious biology that made the plants so interesting also made
them challenging to study with new genetic tools being designed at the
time for more common species with immediate agricultural or medical
relevance. After a decadeslong hiatus while other molecular techniques developed, the project to understand Monophyllaea began again recently
when doctoral student and first author of the research paper Ayaka
Kinoshita joined the lab.

"I believe ours is the only lab in the world currently studying this
species," said Tsukaya.

Understanding what makes Monophyllaea unique required tools that
could see the location and activity level of genes early in the leaf's development. A technique known as whole-mount in situ hybridization
allows researchers to preserve whole chunks of an organism, not just
thin slices, and lock in place all of the genetic material the cells
were using at the time of their death.

The technique is commonly used in animal tissue, but is more complicated
to use in plants because of the stiff outer cell wall around plant cells.

"Luckily, another of our lab members, Assistant Professor Hiroyuki Koga,
is a true professional at using the whole-mount system and he persisted to develop a suitable method for plants," said Tsukaya. Koga is the second
author of the research publication and was able to perfect a technique
to preserve entire three-week-old Monophyllaea plants.

In plants with standard anatomy, the gene SHOOT MERISTEMLESS (STM)
is expressed in cells at the growing tips of stems, referred to as the
shoot meristem.

Additionally, the gene ANGUSTIFOLIA3 (AN3) is expressed in very young
leaves to promote the multiplication of cells that form the leaf.



========================================================================== "With our naked eye, we cannot see any shoot meristem in Monophyllaea. So
we want to know, is it lost or is it modified?" explained Tsukaya.

Instead of separating the location and timing of STM and AN3 gene
expression, young Monophyllaea showed overlapping expression of the two
genes. Researchers say that what looks like a simple leaf in Monophyllaea
is actually a combination or fusing of the shoot meristem and leaf.

"In Monophyllaea, the expression areas overlap, suggesting this plant is
a hybrid of a normal leaf and shoot meristem. We suppose this curious
gene expression pattern is one reason why the plant has such a curious appearance," said Tsukaya.

Researchers state that understanding how unusual species like M. glabra
evolved to use common genes in uncommon ways will help agricultural
scientists develop tools for controlling the size of leaves for optimal
farming cultivation in the future.

"We study M. glabra because the characteristics of Monophyllaea
development are very unique and they cannot be found in any mutants
of common laboratory plants. Dealing with the unique phenomenon can
definitely provide new insights to plant science," said Tsukaya.


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


========================================================================== Journal Reference:
1. Ayaka Kinoshita, Hiroyuki Koga, Hirokazu Tsukaya. Expression
Profiles of
ANGUSTIFOLIA3 and SHOOT MERISTEMLESS, Key Genes for Meristematic
Activity in a One-Leaf Plant Monophyllaea glabra, Revealed by
Whole-Mount In Situ Hybridization. Frontiers in Plant Science,
2020; 11 DOI: 10.3389/ fpls.2020.01160 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200825110744.htm

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