Cold Spring Harbor Laboratory (CSHL) professor David Jackson, Ph.D., and a
team of plant geneticists have identified a gene essential in controlling
development of the maize plant, commonly known in the United States as corn.
The new research extends the growing biological understanding of how the
different parts of maize arise - important information for a plant that is
the most widely planted crop in the U.S. and a mainstay of the global food
supply.

The researchers found that a gene called sparse inflorescence1, or spi1, is
involved the maize plant's synthesis of the growth hormone auxin. This
chemical messenger is familiar to biology students, who learn that it is
produced by the tip of a growing shoot. When the hormone is applied to only
one side of the shoot, that side grows faster, causing the tip to bend.

In a much more complex process, auxin also helps to shape structures such as
leaves or the female organs (ears) and male organs (tassels) of corn. The
initial stages of these structures are called meristems, which consist of
versatile, undifferentiated cells analogous to the stem cells found in
animals. Jackson and colleagues from UC San Diego, including Andrea
Gallavotti who spent one year in Jackson?s lab to perform some of this work,
and at California State University at Long Beach and Pennsylvania State
University, found that meristems emerge from an interplay between the
synthesis of auxin by various cells and its motion between them. Disrupting
either its production (by causing a mutation in the spi1 gene) or its motion
results in stunted, defective organs.

Eudicots vs. Monocots

Much has been learned in the past about organ development in the cress plant
known as Arabidopsis, which biologists regard as a ?model organism? for
plant research, much as the lab mouse has served as a model for research on
mammalian biology. Arabidopsis is in a plant group called eudicots, however,
while maize and many other food crops belong to a group known as monocots.
The spi1 gene has cousins that affect auxin synthesis and organ formation in
Arabidopsis, but there are important differences.

?In maize, spi1 mutations cause severe developmental effects, which is not
the case in Arabidopsis, which we demonstrated by deleting, or
?knocking-out,? genes similar to spi1,? Jackson explained. ?Our work helped
demonstrate that spi1 in maize has evolved a dominant role in auxin
biosynthesis, and is essential for what we plant scientists call
inflorescence development - the process in seed plants in which a shoot
forms that supports the plant?s flowers,? he added.

?When we looked at the interaction between spi1 and genes of the plant that
regulate auxin transport, we found, interestingly, that the transport of
auxin and biosynthesis work together in a synergistic manner to regulate how
the meristem and lateral organs of the maize plant develop.?

?sparse inflorescence1 encodes a monocot-specific YUCCA-like gene required
for vegetative and reproductive development in maize? received advanced
online publication in the Proceedings of the National Academy of Sciences on
September 17, 2008. The complete author list is: Andrea Gallavotti, Solmaz
Barazesh, Simon Malcomber, Darren Hall, David Jackson, Robert Schmidt, and
Paula McSteen. The paper is available at
[dx.doi.org].

About Cold Spring Harbor Laboratory
Cold Spring Harbor Laboratory (CSHL) is a private, not-for-profit research
and education institution at the forefront of efforts in molecular biology
and genetics to generate knowledge that will yield better diagnostics and
treatments for cancer, neurological diseases and other major causes of human
suffering.

For more information, visit www.cshl.edu .