Science - USA (2021-07-09)

and surface deformation of ice [e.g., surface
premelting ( 42 )]. In short, the elastic IMFs
demonstrated here may offer an alternative
platform for exploring ice physics and open
previously unexplored opportunities for ice-
related technology in various disciplines.

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ACKNOWLEDGMENTS
We thank X. K. Zhang, L. Y. Wu, and S. H. Chang at the Center
of Cryo-Electron Microscopy (CCEM), Zhejiang University, for their
technical assistance on cryo-TEM; X. J. Wang at the cryo-EM
facility of Westlake University for the technical assistance on
cryo-FIBM; and L. Yang and Y. Y. Jin for assistance with scattering
spectra analysis. This work was supported by the National Key
Research and Development Project of China (2018YFB2200404),
the National Natural Science Foundation of China (11527901), the

Natural Science Foundation of Zhejiang Province (LR21F050002),

and Fundamental Research Funds for the Central Universities.

Author contributions:L.T., X.G., and Y.R.S conceived of and

supervised the project. P.X. and B.C. performed the experiments.

Y.B., P.X., and B.C. performed the cryo-TEM measurements.

All authors analyzed the data. L.T., X.G., P.X., B.C., and Y.R.S. wrote

the manuscript. All authors discussed the results and commented

on the paper.Competing interests:The authors declare no

competing interests.Data and materials availability:All data are

available in the main text or the supplementary materials.

SUPPLEMENTARY MATERIALS

science.sciencemag.org/content/373/6551/187/suppl/DC1

Materials and Methods

Figs. S1 to S10

Table S1

References ( 43 – 46 )

Movies S1 to S3

6 March 2021; accepted 2 June 2021

10.1126/science.abh3754

PLANT SCIENCE

Cauliflower fractal forms arise

from perturbations of floral gene networks

Eugenio Azpeitia^1 †, Gabrielle Tichtinsky^2 , Marie Le Masson^2 , Antonio Serrano-Mislata^3 ,

Jérémy Lucas^2 , Veronica Gregis^4 , Carlos Gimenez^3 , Nathanaël Prunet5,6, Etienne Farcot^7 ,

Martin M. Kater^4 , Desmond Bradley^8 , Francisco Madueño^3 , Christophe Godin^1 *, Francois Parcy^2 *

Throughout development, plant meristems regularly produce organs in defined spiral, opposite, or whorl

patterns. Cauliflowers present an unusual organ arrangement with a multitude of spirals nested

over a wide range of scales. How such a fractal, self-similar organization emerges from developmental

mechanisms has remained elusive. Combining experimental analyses in anArabidopsis thaliana

cauliflower-like mutant with modeling, we found that curd self-similarity arises because the

meristems fail to form flowers but keep the“memory”of their transient passage in a floral state.

Additional mutations affecting meristem growth can induce the production of conical structures

reminiscent of the conspicuous fractal Romanesco shape. This study reveals how fractal-like

forms may emerge from the combination of key, defined perturbations of floral developmental

programs and growth dynamics.

A

bove-ground plant architectures arise

from the activity of shoot apical meri-

stems (SAMs), pools of stem cells that

give rise to organs such as leaves, shoots,

or flowers. The arrangement of organs

on stems is called phyllotaxis. Plants with a

spiral phyllotaxis usually form two families

of organ spirals that are visible on compact

structures such as flower heads, pine cones,

or cacti (Fig. 1, A to C). These two families of

spirals turn in opposite directions and come

in two consecutive numbers of the Fibonacci

series (Fig. 1A) ( 1 ). In cauliflowers, spiral fam-

ilies are visible not only at one but at several

scales (Fig. 1, D to F). This self-similar organi-

zation culminates in the Romanesco cultivar

in which the spirals appear in relief because of

their conical shape at all scales, a geometrical

feature conferring the whole curd a marked

fractal-like aspect (Fig. 1G).

Cauliflowers (Brassica oleraceavar.botrytis)

were domesticated from cabbages ( 2 ). The

cauliflower inflorescence (the flower-bearing

shoot) takes a curd shape because each emerg-

ing flower primordia never matures to the floral

stage but instead generates more curd-shaped

inflorescences ( 2 , 3 ). InB. oleracea,the genetic

modifications causing curd development are

still debated and likely affect multiple genes

( 2 – 5 ). However, cauliflower-like structures also

exist in the model BrassicaceaeArabidopsis

thalianaand are caused by a double mutation

inAPETALA1(AP1) andCAULIFLOWER(CAL)

(Fig. 1, H and I), two paralogous genes encod-

ing MADS-box transcription factors (TFs) pro-

moting floral development ( 6 , 7 ). TheArabidopsis

molecular regulators governing the develop-

ment of shoots and flowers have been largely

identified ( 8 – 10 ) (table S1). Network models

based on these regulators have been proposed

to explain flower and inflorescence development

( 11 – 14 ). However, whether variants of these net-

works are able to account for the development

ofArabidopsis ap1 calcurds is unknown.

192 9JULY2021•VOL 373 ISSUE 6551 sciencemag.org SCIENCE

(^1) Laboratoire de Reproduction et Développement des Plantes,
Univ. Lyon, ENS de Lyon, UCB Lyon 1, CNRS, INRAE, Inria,
F-69364 Lyon, France.^2 Laboratoire Physiologie Cellulaire et
Végétale, Univ. Grenoble Alpes, CNRS, CEA, INRAE, IRIG-
DBSCI-LPCV, F-38054 Grenoble, France.^3 Instituto de
Biología Molecular y Celular de Plantas (IBMCP), Consejo
Superior de Investigaciones Científicas (CSIC) - Universidad
Politécnica de Valencia (UPV), 46022 Valencia, Spain.
(^4) Dipartimento di Bioscienze, Università degli Studi di Milano,
20133 Milan, Italy.^5 Division of Biology and Biological
Engineering, California Institute of Technology, Pasadena,
CA 91125, USA.^6 Department of Molecular, Cell and
Developmental Biology, University of California, Los Angeles,
CA 90095, USA.^7 School of Mathematical Sciences,
University of Nottingham, Nottingham NG7 2RD, UK.
(^8) Department of Cell and Developmental Biology, John Innes
Centre, Norwich NR4 7UH, UK.
*Corresponding author. Email: [email protected] (C.G.);
[email protected] (F.P.)†Present address: Centro de
Ciencias Matemáticas, Universidad Nacional Autónoma de México,
Morelia, México.
RESEARCH | RESEARCH ARTICLES