November 17, 2008
Source:
Public Library of Science
Why do poppies and sunflowers grow
as a single flower per stalk while each stem of a tomato plant
has several branches, each carrying flowers? In a new study,
published in this week's issue of the open access journal
PLoS Biology, Dr. Zachary Lippman and colleagues identify a
genetic mechanism that determines the pattern of flower growth
in the Solanaceae (nightshade) family of plants that includes
tomato, potato, pepper, eggplant, tobacco, petunia, and deadly
nightshades. Manipulation of the identified pathway can turn the
well known tomato vine into a highly branched structure with
hundreds of flower-bearing shoots, and may thereby result in
increased crop yields.
While the development of individual flowers is well understood,
the molecular mechanisms that determine the architecture of
inflorescences - flower-bearing shoots - are not. The way that
inflorescences branch determines the number and distribution of
flowers; in peppers (capsicum) inflorescences do not branch, so
flowers are singular; in tomatoes, inflorescence branching is
repetitive and regular, forming a zigzagged vine The tomato
mutants anantha (an) and compound inflorescence (s) have long
been known to produce large numbers of branches and flowers, and
the new work elucidates the underlying genetics.
Dr. Lippman, and a team of researchers drawn from three
institutions in Israel, investigated inflorescence branching by
studying these mutant tomato plants. They identified the genes
responsible: the anantha (AN) and compound inflorescence (S)
genes. S is a member of the well known homeobox gene family,
which plays a crucial regulatory role in patterning both animals
and plants. Lippman et al. have shown that manipulation of these
genes in tomato plants can dramatically alter the architecture
and number of inflorescences, and that altered activity of AN in
pepper plants can stimulate branching. Variation in S also
explains the branching variation seen in domestically grown
tomato strains.
The two genes work in sequence to regulate the timing of
development of a branch and a flower – so, for example, slowing
down the pathway that makes a flower allows for additional
branches to grow. While this study by Lippman et al. focuses on
variations in particular nightshades, the insight leads to a new
understanding of how many plants, such as trees, control their
potential to branch.
The making of a compound inflorescence in tomato and related
nightshades
Lippman ZB, Cohen O, Alvarez JP, Abu-Abied M, Pekker I, et
al. (2008)
PLoS Biol 6(11): e288. doi:10.1371/journal.pbio.0060288
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