Science - USA (2021-12-10)

and blade morphogenesis, consistent with the

19th-century view of homology (Fig. 1K). Other

anatomical traits, such as venation patterns,

may represent further elaborations rather than

being primary indicators of homology. Our

findings are comparable to those from animal

evo-devo studies, in which a discarded hypoth-

esis, the notion that the ventral side of insects

corresponds to the dorsal sides of vertebrates,

was reinstated in the light of fresh develop-

mental genetic evidence ( 37 ). We further provide

a mechanistic link between the developmental

genes involved and their morphogenetic effects.

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ACKNOWLEDGMENTS

We thank D. O’Connor, members of the Coen laboratory,

C. Whitewoods, members of the Hake laboratory, S. Leiboff,

C. L. Shaw, and A. Hudson for support and helpful discussions;

T. Dao for help with the PI staining and tissue clearing method; and

the microscopy and greenhouse staff at the JIC and the USDA

and the Cornell Institute of Biotechnology’s Imaging Facility.

Funding:This work was supported by a bilateral NSF/BIO-BBSRC

grant (BB/M023117/1 to S.H. and E.C.); the BBSRC (grants

BBS/E/J/000PR9787, BBS/E/J/00000152, BB/L008920/1, and

BBS/E/J/000PR9789 to E.C.); and the NSF (grant DEB-1457070

to M.S.). H.K. received funding from the Chinese Academy of

Sciences (grants XDB27010304 and ZDBS-LY-SM022) for J.C. A.R.

is funded by University of Edinburgh start-up funds. The Cornell

1380 10 DECEMBER 2021¥VOL 374 ISSUE 6573 science.orgSCIENCE

Fig. 4. Eudicot leaf models.(A) PZ (dotted line) straddles the midplane (green line) between the abaxial
(orange) and adaxial (blue) domains. (B) PZ central (blue), lateral (light red), outer lateral (dark red), and marginal
(cyan) domains. (CtoK) Volumetric primordium emergence models. (C) and (D) are the wild type, (E) and (F) are
prs, (G) and (H) areprs wox1, and (I) to (K) are the abaxialized mutant. Blue arrows indicate proximodistal
polarity, asterisks the presumptive midvein tip, and“A”the apex. Arrowhead indicates the missing domains.
(LtoU) Tissue sheet models. Upper leaf domains are shown in orange and purple. (L) to (O) are the petiole-
sheath hypothesis. (P) to (S) are the petiole-leaf hypothesis. (N) and (R) SHEATH identity (dark gray overlay,
bracket) introduced at P4. In (T) and (U), theprs wox1mutant generates a narrow petiole base in the petiole-leaf
model (T) and a narrow leaf in the petiole-sheath model (U). Arrowhead indicates the missing domains. (V) is
ZmTRU1 immunolocalization on a maize vegetative shoot apex longitudinal section (n= 4). Arrowhead indicates
theligule.P1toP6aretheprimordiaplastochrons.Scalebar,100mm. Asterisk indicates presumptive midvein tip.

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