The mystery of how a major plant hormone works to defend plants
against invaders has been revealed, thanks to collaborative research efforts
by Michigan State University and Washington State University.
While scientists have known for years that a common plant hormone,
jasmonate, plays a crucial role in plant development and function, the steps
that convert the hormone?s signal into genetic and cellular action have
remained elusive. MSU scientists Sheng Yang He and Gregg Howe were part of
two back-to-back discoveries that solved the mystery, described in the July
18 online issue of the journal Nature.

Jasmonate is the last major plant hormone to have its signaling
process revealed. Initial research by WSU researchers identified the family
of proteins ? dubbed JAZ proteins ? that are critical to plants receiving
and responding to the jasmonate signal.

?In a healthy environment, these JAZ proteins are doing their job ?
they?re blocking all the defenses and signals, because they are not needed,?
said Howe, an MSU professor of biochemistry and molecular biology. ?But when
a plant becomes stressed by an insect or pathogen, the plant needs to
respond very quickly if it?s going to be successful in warding off the
attacker.?

Independent of the WSU work, Howe and He used Arabidopsis, a common
lab plant, and tomato plants to determine how the JAZ proteins work. Their
experiments showed that the jasmonate signal causes direct interaction
between JAZ proteins and a second protein complex, SCFCOI1, that works to
eliminate the JAZ protein so that the plant can mount a defense response.

Based on the research findings, there is strong evidence to suggest
that Howe and He might have identified the SCFCOI1 protein complex as the
receptor for jasmonate.

?We found that when jasmonate is present the COI1 and JAZ proteins
bind together,? said He, an MSU professor of plant biology, plant pathology,
and microbiology and molecular genetics. ?This opens the way for the plant
to turn on the necessary genetic or cellular response.?

As part of their research, Howe and He have proposed a model for how
this interaction works.

?Now that we know what the active signals are and have identified the
key regulatory proteins ? the JAZ proteins ? involved, the hope is to either
genetically modify plants or develop compounds that mimic the jasmonate
hormone,? Howe said. ?The research may help scientists engineer plants for
increased resistance to insects and pathogens.?

Researchers at both universities will continue to work on other
critical aspects of this research.

?Understanding how the jasmonate system works will shed light on all
the processes in which the hormone is involved, notably plant reproduction
and defense,? said John Browse, head of the WSU Institute of Biological
Chemistry research team.

?This study represents a significant advance in our understanding of a
major plant hormone and how it works,? He said. ?We are excited to be part
of this collaborative effort and look forward to extending the understanding
and application of this important work.?

The research was funded by the National Institutes of Health and the
U.S. Department of Energy and supported by the Michigan Agricultural
Experiment Station.


[www.msu.edu]