Environmental Engineering Reference
In-Depth Information
FIGure 23.3
Variation in the growth habit of Brachypodium. Two Turkish inbred lines with erect (left) and
spreading (right) growth habits are shown.
in a GA response repressor in wheat (Peng et al. 1999). The resulting disruptions in GA synthesis
and signaling enabled the shorter varieties to resist lodging, or falling over, and to channel applied
nitrogen fertilizer to grain production rather than stem growth (Evans 1993; Conway 1997; Sasaki
et al. 2002; Hedden 2003). The converse goal of increasing vegetative biomass might be achieved
through the opposite approach, i.e., upregulating GA biosynthesis and/or de-repressing GA growth
responses (Sasaki et al. 2002; Fernandez et al. 2009).
The dwarfing alleles in hexaploid, Green Revolution wheat correspond to the
Rht-B1
/
Rht-D1
genes, which encode DELLA-motif containing proteins (Peng et al. 1999). A loss-of-function
mutation in the orthologous rice gene
SLR1
results in increased plant height (Ikeda et al. 2001).
BLAST searches of the Brachypodium genome revealed that Brachypodium, like rice, contains a
single DELLA-encoding gene and that the Brachypodium DELLA protein exhibits 86% amino-
acid identity to
SLR1
; this finding suggests that the mechanisms governing GA-regulated growth
responses are likely to be similar in Brachypodium and the other grasses. Components of the GA
pathway and additional candidate genes of interest can be easily identified, cloned, and functionally
characterized in Brachypodium thanks to a sequenced genome and an efficient transformation
protocol. Brachypodium's short life-cycle and simple growth requirements will further facilitate
rapid hypothesis testing for genetic manipulations aimed at improving biofuels feedstocks.
23.5.2 f
actorS
i
influEncing
B
iomaSS
q
uantity
:
i
ntEractionS
with
thE
E
nvironmEnt
In addition to morphological characteristics, a plant's interactions with the environment also affect
biomass yield. Thus, adaptability to a range of soil conditions, efficient water and nutrient use, and
resistance to abiotic and biotic stresses are all desirable traits in a bioenergy crop (DOE 2007). For
investigating these traits, Brachypodium also provides a wealth of resources. The geographical
range of Brachypodium encompasses a diversity of habitats (Garvin et al. 2008; Opanowicz
et al. 2008; Vogel et al. 2009), providing the opportunity to investigate adaptations to different
environments with a genetically tractable organism. The first proposal of Brachypodium as a model
grass included the observation that different Brachypodium ecotypes varied in their responses to
the agriculturally important fungal pathogens
Puccinia striformis
f. sp.
triticae
and
Magnaporthe
grisea
, the causative agents of wheat yellow stripe rust and rice blast, respectively (Draper et al.
2001). Infections with
Fusarium graminearum
(head blight) (D. Garvin, personal communication)
