Research gets to the heart of organ shape in nature

Date:
August 13, 2020
Source:
John Innes Centre
Summary:
Researchers have shed fresh light on the evolution and function
of the shapes we see in nature - using as a model the heart shaped
fruits of the Capsella genus.



FULL STORY ========================================================================== Researchers have shed fresh light on the evolution and function of the
shapes we see in nature -- using as a model the heart shaped fruits of
the Capsella genus.


==========================================================================
The natural world is full of diverse shapes from organs to whole organisms
that are fitted by evolution to perform and reproduce optimally in
their environment.

The Capsella seed pods with their distinctive heart-shaped shoulders offer
an anatomical novelty and an excellent study system for understanding
the diversity of shapes.

Earlier studies have shown that the expression of key regulatory genes
is a primary driver in controlling shape evolution in organs. This new
study carried out by John Innes Centre researchers adds another critical
step in this pathway by revealing a modification of protein activity
that is critical for organ- shape formation.

They show that the SUMO-protease HEARTBREAK (HTB) from Capsella
rubella controls the activity of the key regulator of fruit development INDEHISCENT via a process called de-SUMOylation.

Only via this de-SUMOylation -- a kind of molecular trimming activity --
is a pathway activated which allows biosynthesis of the plant hormone
auxin which in turn facilitates anisotropic cell expansion to form the heart-shaped Capsella fruit.



========================================================================== Professor Lars O/stergaard a programme leader at the John Innes Centre
and corresponding author of the paper explains the significance: "We
know that the diversity in shape we observe in nature frequently is
caused by changes in the position and timing of key regulatory genes:
that is how a lot of variation occurs.

"What we have found is that there is this post translational effect,
beyond the gene expression. This protein modification is at the basis
of this type of diversity of fruit shape -- and goes a long way to
explain the difference for example between the fruits of Capsella
and those from the related model plant Arabidopsis. This is about a modification of protein activity at a different stage than we have seen before." Researchers used forward genetic screening -- a technique to
study a range of traits -- which identified a mutant with compromised development of the heart- shaped fruit. The mutant was therefore named, heartbreak. They used time-lapse 3D imaging and molecular genetics to characterise the heartbreak phenotype at the cellular and molecular level.

First author Dr Yang Dong added: "We now have an entire pathway based on
gene expression, hormone dynamics and post translational modification
of proteins in such detail that we can test to what extent these kinds
of pathways with these components are shared much wider across kingdoms
and not just within the plant kingdom." One of the next steps for the researchers is to is to translate this fundamental discovery from the
research plant Capsella to the related commercial crop oilseed rape.

The research answers a key question about how these shapes appear.

But why does nature come up with such an unusual shape as the heart-shaped
pods of Capsella? What is the function behind this form? The reason is
still debatable, explains Professor O/stergaard.

"Previously we thought these shapes might be a good functional design for
seed dispersal because the shape could allow the wind to catch the seed
pod walls, but our assays comparing them with Arabidopsis and oilseed
rape do not reveal any great advantage of the Capsella fruit in seed
dispersal. So, we don't think that can be a major factor.

"It is possible they could act like solar panels. In other words,
maybe they function to capture sunlight and increase photosynthetic
capacity. We know that the photosynthetic capacity of the seed pod
walls can have a strong effect on seed development inside the pod and
therefore on yields. So, by understanding this mechanism it does give
us tools to perhaps be able to manipulate the seed pod walls in crops
like oilseed rape."

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


========================================================================== Journal Reference:
1. Yang Dong, Mateusz Majda, Jan Simura, Robert Horvath, Anjil K.

Srivastava, Łukasz Łangowski, Tilly Eldridge, Nicola
Stacey, Tanja Slotte, Ari Sadanandom, Karin Ljung, Richard S. Smith,
Lars O/ stergaard. HEARTBREAK Controls Post-translational
Modification of INDEHISCENT to Regulate Fruit Morphology in
Capsella. Current Biology, 2020; DOI: 10.1016/j.cub.2020.07.055 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200813142327.htm

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