West Lafayette, Indiana
December 17, 2008
Purdue University researchers found a mechanism that
naturally shuts down cellulose production in plants, and
learning how to keep that switch turned on may be key to
enhancing biomass production for plant-based biofuels.
Nicholas Carpita, a professor of botany and plant pathology,
said that small-interfering RNAs (siRNAs) play a normal role in
plant development by shutting off genes involved in primary cell
wall growth in order to begin development of thicker, secondary
cell walls.
"These small RNAs were known to play a role in fending off
disease-causing pathogens, but we are only now beginning to
understand their involvement in normal plant development," he
said.
Carpita's research team reported its findings in Monday's (Dec.
15) early online issue of the Proceedings of the National
Academy of Sciences.
"If we can learn to interfere with the down-regulation of
cellulose synthesis, then plants may be able to produce more
cellulose, which is key to biofuels production," Carpita said.
Mick Held, a postdoctoral researcher in Carpita's lab,
virologist Steve Scofield, a U.S. Department of Agriculture
research scientist and adjunct assistant professor of agronomy
at Purdue, and Carpita made the discovery in barley after
introducing a virus as a way to "silence" specific genes and
study their functions. The researchers noticed that the virus
had more effect then anticipated.
"The virus hijacked a whole suite of genes, and when we compared
the targeted plant to our control plants we found that the small
RNAs were responsible and already in the controls even without
adding the virus," Held said.
Carpita said this let researchers see that the siRNAs - among
other things - regulate and shut down primary cell wall
development to begin secondary wall growth.
"These secondary stages result in characteristics such as tough
rinds of corn stalks, vascular elements to conduct water and
fibers for strength," he said.
The researchers said that delaying or preventing the shutdown of
both primary and secondary cellulose production might enhance
total plant biomass.
"Most biofuel researchers believe that cellulose utilization
offers the best path to sustainable ethanol production,"
Scofield said. "Our work uncovered a previously unknown
mechanism that suggests a way to increase the amount of
cellulose produced in plants."
Other members of the research team were Bryan Penning and Sarah
Kessans of Purdue and Amanda Brandt of the USDA/Ag Research
Service, Crop Production and Pest Control Research Unit located
at Purdue.
The research was funded by a U.S. Department of Energy, Energy
Biosciences grant.
Writer: Beth Forbes
ABSTRACT
Small-interfering RNAs
from Natural Antisense Transcripts Derived from a Cellulose
Synthase Gene Modulate Cell Wall Biosynthesis in Barley
Michael A. Held, Bryan Penning, Amanda S. Brandt, Sarah
A. Kessans, Weidong Yong, Steven R. Scofield, and Nicholas
C. Carpita
Small-interfering RNAs (siRNAs) from natural cis-antisense
pairs derived from the 3_-coding region of the barley
(Hordeum vulgare) CesA6 cellulose synthase gene
substantially increase in abundance during leaf elongation.
Strand-specific RT-PCR confirmed the presence of an
antisense transcript of HvCesA6 that extends >1230 bp from
the 3_ end of the CesA-coding sequence. The increases in
abundance of the CesA6 antisense transcript and the 21-nt
and 24-nt siRNAs derived from the transcript are coincident
with the down-regulation of primary wall CesAs, several Csl
genes, and GT8 glycosyl transferase genes, and are
correlated with the reduction in rates of cellulose and (1 3
3),(1 3 4)-_-D-glucan synthesis. Virus-induced gene
silencing using unique target sequences derived from HvCesA
genes attenuated expression not only of the HvCesA6 gene,
but also of numerous nontarget Csls and the distantly
related GT8 genes and reduced the incorporation of D-14C-Glc
into cellulose and into mixed-linkage (1 3 3),(1 3
4)-_-D-glucans of the developing leaves. Unique target
sequences for CslF and CslH conversely silenced the same
genes and lowered rates of cellulose and (1 3 3),(1 3
4)-_-D-glucan synthesis. Our results indicate that the
expression of individual members of the CesA/Csl superfamily
and glycosyl transferases share common regulatory control
points, and siRNAs from natural cis-antisense pairs derived
from the CesA/Csl superfamily could function in this global
regulation of cell-wall synthesis.
|
|
