Scientists solve the grass leaf conundrum

Date:
December 9, 2021
Source:
John Innes Centre
Summary:
The mystery of grass leaf formation has now been unraveled using the
latest computational modelling and developmental genetic techniques.



FULL STORY ========================================================================== Grass is cut regularly by our mowers and grazed on by cows and sheep,
yet continues to grow back. The secret to its remarkable regenerative
powers lies in part in the shape of its leaves, but how that shape arises
has been a topic of longstanding debate.


==========================================================================
The debate is relevant to our staple crops wheat, rice and maize,
because they are members of the grass family with the same type of leaf.

The mystery of grass leaf formation has now been unravelled by a John
Innes Centre team, in collaboration with Cornell University and the
University of California, Berkley, and the University of Edinburgh using
the latest computational modelling and developmental genetic techniques.

One of the corresponding authors Professor Enrico Coen said of the
findings which appear in Science: "The grass leaf has been a conundrum. By formulating and testing different models for its evolution and development we've shown that current theories are likely incorrect, and that a
discarded idea proposed the 19th century is much nearer the mark."
Flowering plants can be categorised into monocots and eudicots. Monocots,
which include the grass family, have leaves that encircle the stem at
their base and have parallel veins throughout. Eudicots, which include brassicas, legumes and most common garden shrubs and trees, have leaves
that are held away from the stem by stalks, termed petioles, and typically
have broad laminas with net-like veins.

In grasses, the base of the leaf forms a tube-like structure, called the sheath. The sheath allows the plant to increase in height while keeping
its growing tip close to the ground, protecting it from the blades of lawnmowers or incisors of herbivores.

In the 19th Century, botanists proposed that the grass sheath was
equivalent to the petiole of eudicot leaves. But this view was challenged
in the 20th century, when plant anatomists noted that petioles have
parallel veins, similar to the grass leaf, and concluded that the entire
grass leaf (except for a tiny region at its tip) was derived from petiole.

Using recent advances in computational modelling and developmental
genetics, the team revisited the problem of grass development. They
modelled different hypotheses for how grass leaves grow, and tested the predictions of each model against experimental results. To their surprise,
they found that the model based on the 19th century idea of sheath-petiole equivalence was much more strongly supported than the current view.

This mirrors findings in animal development where a discarded theory
-- that the 'underbelly' side of insects corresponds to the back of
vertebrates like us -- was vindicated in the light of fresh developmental genetic research.

The grass study shows how simple modulations of growth rules, based on a
common pattern of gene activities, can generate a remarkable diversity
of different leaf shapes, without which our gardens and dining tables
would be much poorer.

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


========================================================================== Journal Reference:
1. A. E. Richardson, J. Cheng, R. Johnston, R. Kennaway, B. R. Conlon,
A. B.

Rebocho, H. Kong, M. J. Scanlon, S. Hake, E. Coen. Evolution
of the grass leaf by primordium extension and petiole-lamina
remodeling. Science, 2021; 374 (6573): 1377 DOI:
10.1126/science.abf9407 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211209142548.htm

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