Upton, New York
April 10, 2009
 By
creating a “family tree” of genes expressed in one form of woody
plant and a less woody, herbaceous species, scientists at the
U.S. Department of Energy’s
Brookhaven National Laboratory have uncovered clues that may
help them engineer plants more amenable to biofuel production.
The study, published in the April 2009 issue of Plant Molecular
Biology, also lays a foundation for understanding these genes’
evolutionary and structural properties and for a broader
exploration of their roles in plant life.
“We are studying a very large family of genes that instruct
cells to make a variety of enzymes important in a wide range of
plant functions,” said Brookhaven biologist Chang-Jun Liu
(photo). By searching the genomes of woody Poplar trees and
leafy Arabidopsis, the scientists identified 94 and 61 genes
they suspected belonged to this family in those two species,
respectively. They then looked at how the genes were expressed —
activated to make their enzyme products — in different parts of
the plants. Of particular interest to Liu’s group were a number
of genes expressed at high levels in the woody plant tissues.
“Wood and other biofibers made of plant cell walls are the most
abundant feedstocks for biofuel production,” explained Liu. “One
of the first steps of biofuel production is to break down these
biofibers, or digest them, to make sugar.”
But plants have strategies to inhibit being digested. For
example, Liu explained, small molecules called acyl groups
attached to cell-wall fibers can act as barriers to hinder
conversion of the fibers to sugar. Acyl groups can also form
cross-linked networks that make cell walls extra strong.
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“Our long-term interest is to find
the enzymes that control the formation of cell-wall-bound acyl
groups, so we can learn how to modify plant cell walls to
increase their digestibility,” Liu said. “The current study, a
thorough investigation of an acyl-modifying enzyme family,
provides a starting point for us to pursue this goal.”
In fact, some of the genes the scientists found to be expressed
at high levels in woody tissues may carry the genetic
instructions for making the enzymes the scientists would like to
control.
“Our next step will be to use biochemical and biophysical
approaches to characterize these individual genes’ functions to
find those directly or indirectly related to cell-wall
modification. Then we could use those genes to engineer new
bioenergy crops, and test whether those changes improve the
efficiency of converting biomass to biofuel,” Liu said.
Liu’s group also made some interesting observations about gene
expression and gene location in their study of the
acyl-modifying enzyme genes. “We discovered a few unique pairs
of genes that were inversely overlapped with their neighboring
genes on the genome,” Liu said. In this unique organization, the
paired genes (sequences of DNA) produce protein-encoding
segments (RNAs) that are complementary to one another — meaning
the two RNA strands would stick to each other like highly
specific Velcro. That would prevent the RNA from building its
enzyme, so the expression of one gene in the pair appears to
inhibit its partner.
Perhaps understanding this natural “anti-sense” regulation for
gene expression will assist scientists in their attempts to
regulate acyl-modifying enzyme levels.
This work was supported by the DOE-Department of Agriculture
joint Plant Feedstock Genomics program and by Brookhaven’s
Laboratory Directed Research and Development program. Funding
was also provided by DOE’s Office of Science. In addition to
Liu, Xiao-Hong Yu, a former postdoctoral research associate, and
Jinying Gou, a current postdoc, contributed to this work. |
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