function relationship of ESF1 is consistent with
other cysteine-rich peptides, such as those involved
in cell signaling of the stomatal cell lineage (24),
and further supports their signaling role during early
embryogenesis. Moreover, we argue that ESF1
regulation of early suspensor growth arose from
parental conflict (35) and provides a maternal
advantage over embryo growth at a critical stage
when parental investment determines the fate of
the offspring. ESF1 peptides are not imprinted
like the related maternally expressed MEG1 peptides in maize (8, 36), but are maternally deposited
in the central cell gamete and early in the endosperm, which may be indicative of their immediate requirement at the onset of fertilization. Thus,
plants appear to have evolved multiple independent
strategies in the form of embryonic and extraembryonic factors, including mobile RNAs and peptides, to maternally control early embryogenesis.
All plant material used in this study was derived
from the wild-type Columbia (Col-0) accession
and mutant alleles cdka;1 (30), kpl-1 (31), ssp-2
(28), CA-YDA, and yda-2991 (29). Details of transgenic lines can be found in the supplementary
materials and methods. Microarray analysis was
performed on wild-type developing siliques collected after manual pollination (14). Quantitative
polymerase chain reaction analysis was performed
as described in the supplementary materials and
methods, with oligonucleotides listed in table S6.
Details of histochemical and structural biochemical analyses of ESF1 peptides are fully described
in the supplementary materials and methods. Sequence of the codon-optimized synthetic ESF1
gene constructs is listed in table S7.
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Acknowledgments: We thank H. Prescott, A. Sarmiento,
D. Garcia, and E. Caamaño for technical assistance. We also thank
T. Laux, W. Lukowitz, I. Moore, B. Scheres, A. Schnittger, M. Bayer,
and D. Weijers for seed stocks and valuable suggestions. We
acknowledge funding from the Royal Society, ESF/RTD Framework
COST action (FA0903), and Biotechnology and Biological Sciences
Research Council grants (BB/F008082, BB/L003023/1 and
BB/L003023). The work at the University of Minnesota was supported
by NSF award IOB-0516811. NMR experiments were partly
supported by Nanotechnology Platform Program of the Ministry of
Education, Culture, Sports, Science and Technology (MEXT), Japan.
K.S. and M. T. acknowledge the Minnesota Supercomputing Institute
for computational resources and systems support used in microarray
analysis. M. T. and K.S. performed microarray experiments and
data analysis. E.M validated the array data, generated most
transgenic lines, and conducted genetic analyses. L.M.C designed and
performed genetic experiments, generated the LhG4 transactivation
lines, and performed immunodetection. S.L.O. and R.P. performed
the ovule culture experiments. K.B. identified the suspensor-specific
At2g30560 gene and generated pGRP-GUS:GFP lines. M.M. expressed
ESF1 peptides. M.M., Y.U. and S.O. purified synthetic wild-type and
mutant ESF1 peptides and performed solution NMR structural
analysis. J.G-M., K. V., S.O., and M.M. conceived and supervised the
study. J.G-M. and L.M.C. wrote the paper with input from S.O. All
authors have reviewed and approved the paper, and the authors
disclose no conflicts of interest.
Materials and Methods
Figs. S1 to S13
Tables S1 to S7
10 July 2013; accepted 4 March 2014
Flies Evade Looming Targets
by Executing Rapid Visually
Directed Banked Turns
Florian T. Muijres,1 Michael J. Elzinga,1 Johan M. Melis,1,2 Michael H. Dickinson1*
Avoiding predators is an essential behavior in which animals must quickly transform sensory
cues into evasive actions. Sensory reflexes are particularly fast in flying insects such as flies, but the
means by which they evade aerial predators is not known. Using high-speed videography and
automated tracking of flies in combination with aerodynamic measurements on flapping robots,
we show that flying flies react to looming stimuli with directed banked turns. The maneuver
consists of a rapid body rotation followed immediately by an active counter-rotation and is enacted
by remarkably subtle changes in wing motion. These evasive maneuvers of flies are substantially
faster than steering maneuvers measured previously and indicate the existence of sensory-motor
circuitry that can reorient the fly’s flight path within a few wingbeats.
Flies are among the most agile flying ani- mals and have served as a model for many features of sensory physiology (1), muscle
mechanics (2, 3), and aerodynamics (4–7).
Among their most impressive flight behaviors
are evasive maneuvers, as witnessed by anyone
who has attempted to swat them. The evasive
takeoff behaviors of flies have been thoroughly
investigated, and evidence suggests that they can
quickly determine the direction of a looming threat
and bias their jump in the opposite direction (8).
Although the escape maneuvers of flying flies
have recently been observed (9), they have not
been systematically analyzed and it is not known
whether, or how, they detect and evade a rapidly
Like aircraft, the angular orientation of a flying insect can be specified by its rotation about
three orthogonal axes: the yaw, pitch, and roll
axes (Fig. 1C). For an insect flying steadily, the
yaw axis is vertical, whereas the pitch and roll
axes lie in the horizontal plane. Yaw—that is,
rotation about the yaw axis—will simply change
a fly’s orientation in the horizontal plane. Pitch
will cause the head to tilt either up or down,
whereas roll will cause the body to rotate to the
left or right. A combination of both roll and pitch
will bank the body with respect to the horizontal
plane. Previous studies suggest that flies change
course without banking by creating torque about
their yaw axis (10–12). It is not known, however,
whether flies or other insects employ this same
strategy during fast evasive maneuvers.
1University of Washington, Box 351800, 24 Kincaid Hall, Seattle,
WA 98195–1800, USA. 2Faculty of Aerospace Engineering, Delft
University of Technology, 2600 GB Delft, Netherlands.
*Corresponding author. E-mail: email@example.com