Brachypodium - Bioenergy Crop Plants - page 599

thus provides an excellent resource for investigating natural diversity. The oldest collection consists
of approximately 30 population samples dating back to the 1940s. These accessions are available
from the U.S. Department of Agriculture (USDA) National Plant Germplasm System (NPGS)
(www.ars-grin.gov/npgs/), and relevant passport data can be accessed at www.brachypodium.org.
Twenty-seven of the NPGS accessions, 5 diploid and 22 polyploid, were used to generate inbred
lines (designated with the prefix “Bd”) that are freely available to the research community (Vogel
et al. 2006b). The diploid inbred lines include two lines [Bd21, the line used for genome sequencing,
and Bd21-3, which was selected for efficient transformation (Vogel and Hill 2008)] that were
derived from the same NPGS accession, PI 254867. These lines are genetically distinct and, thus,
presumably were derived from different individuals collected at the same location (Vogel et al.
2009). Another collection of diploid and polyploid ecotypes (designated “ABR”) is maintained at the
University of Wales, Aberystwyth. Some of the ABR ecotypes are unique, whereas others overlap
with material in the NPGS collection. Synonymous ABR and NPGS designations are listed at www.
brachypodium.org/stocks. A material transfer agreement governs the use of all ABR ecotypes.
Recently, 188 diploid inbred lines and a smaller number of polyploid inbred lines were generated
from seeds collected at 53 sites across Turkey; these lines are being freely distributed to the research
community (Filiz et al. 2009; Vogel et al. 2009). Inbred lines from seeds collected by M. Tuna were
designated with a prefix corresponding to the first three letters of the collection location (e.g., “Tek”
for the nearby town of Tekirdag) (Vogel et al. 2009). Lines from seeds collected by H. Budak were
grouped based on phenotypic similarity and labeled with the prefix “BdTR” followed by the group
number and a letter to designate the specific line (Filiz et al. 2009). To survey the genetic diversity
of these newly generated lines, 43 simple sequence repeat (SSR) markers were used to genotype the
lines, together with the six previously generated diploid inbred lines (Bd1-1, Bd2-3, Bd3-1, Bd18-1,
Bd21, and Bd21-3) (Vogel et al. 2009). The SSR marker profiles were used to create an unrooted
phylogenetic tree (Figure 23.2) (Vogel et al. 2009). Interestingly, lines that had been assigned to
each BdTR group on the basis of phenotypic similarities clustered together in genetically related
groups on the tree despite originating from many different locations. Conversely, lines originating
from one location were often genetically distinct. Taken together, these data suggest that there is
a significant amount of long-distance seed dispersal. The phylogenetic tree strongly supported a
clade containing Bd1-1, the BdTR7 and BdTR8 groups, and the Tek accessions. These lines also
shared similar phenotypes, including long vernalization requirement and small, nearly hairless
seeds (Figure 23.2) (Vogel et al. 2009).
Diploid Brachypodium accessions have obvious phenotypic differences indicating that they can
be exploited to study a number of traits relevant to biomass crop development. The diversity in the
flowering times and vernalization requirements of Brachypodium lines is particularly striking. After
2-4 weeks of vernalization, the diploid inbred lines Bd2-3, Bd3-1, Bd21, and Bd21-3 flower relatively
rapidly, within 2-3 weeks, under greenhouse conditions, whereas the Bd18-1 and Bd1-1 lines flower
much later, even after longer vernalization (Vogel et al. 2006b, 2009). For some Bd lines (Bd2-3, Bd3-1,
Bd21, and Bd21-3) extending the day length to 20 h eliminates the need for vernalization (Vogel et al.
2006b, 2009; Vogel and Hill 2008). Very long days do not trigger rapid flowering in any of the new
Turkish inbred lines (Vogel et al. 2009). The Tek inbred lines, originating from northern Turkey, are
especially late flowering and require 8-16 weeks of vernalization (Vogel et al. 2009). The molecular
mechanisms underlying flowering-time regulation in Brachypodium are currently unknown. A
report that expression of the floral repressor Terminal Flower 1 from perennial ryegrass, Lolium
perenne , delays flowering in Brachypodium provides a starting point for future molecular-genetic
studies (Olsen et al. 2006). Additionally, a recent analysis of inbred lines with diverse flowering times
suggests that the putative Brachypodium VERNALIZATION2 and VERNALIZATION3 genes are
involved in controlling flowering time (Schwartz et al. 2010). Other phenotypic differences between
lines include the presence or absence of hairs and the number and angle of inflorescence branches
(Opanowicz et al. 2008; Filiz et al. 2009; Vogel et al. 2009). Accessions also vary in the degree
to which the seed disarticulates from the inflorescence, an agriculturally important trait known as