Agriculture Reference
In-Depth Information
as a collection of objects that equate to leaf, stem,
root, and seed components (Sequeira et al., 1991,
1997). Recent attempts have begun to incorporate
the phytomer approach of building plant canopies
into the object-oriented design that can also be
scaled up, or aggregated, into lower levels of reso-
lution, such as the seed component of earlier
designs (Drouet and Pages 2007; Hargreaves and
McMaster 2008).
barley, and other cereal crops. Although the
genetic pathway controlling fl owering is qualita-
tively well established, few attempts have been
made to predict the time of fl owering for plants
in the fi eld based on which loci are present and
how gene expression responds to the environ-
ment. An effort showing promise is using the
specifi c alleles of the vernalization, photoperiod,
and earliness
per se
genes to establish the param-
eters in predicting wheat phenology in the fi eld
(White 2006; White et al., 2008). Earlier efforts
using neural networks for fl owering time of Ara-
bidopsis may also provide alternative approaches
for determining wheat fl owering time (Welch
et al., 2003).
Incorporation of semidwarfi ng genes was essen-
tial for the Green Revolution, and molecular
biology is adding greater insight into the vari-
ability and functioning of different semidwarfi ng
genes. Functional orthologues of the
GAI
genes
of Arabidopsis have been identifi ed for wheat (the
Rht
genes) and other cereal crops. Some efforts
have been made to incorporate this knowledge
into wheat simulation modeling of plant height
(Baenziger et al., 2004).
While other similar examples could be made of
new insights emerging from identifying genes and
their function and linking the genes to wheat
development and modeling (Fowler et al., 1999),
most examples have focused on known genes that
appear to have more limited genetic pathways
controlling the developmental process. With
increasing complexity of the genetic pathway
controlling a trait, quantitative expression of mul-
tiple genes and their response to the environment
currently seems nearly intractable given our
current understanding. Some overviews of these
challenges are discussed elsewhere (White and
Hoogenboom 2003; Edmeades et al., 2004; White
et al., 2004a,b; Hammer and Jordan 2007; Yin and
Struik 2007).
One area where the linkage between molecular
biology and wheat development is poorly under-
stood involves the plastochron and phyllochron.
Given the variation among cultivars in these
traits, and particularly the difference between
spring and winter wheat genotypes, this has
considerable impact on our understanding and
LINKING MOLECULAR BIOLOGY
AND FUNCTIONAL GENOMICS
TO DEVELOPMENT
Since sequencing of the model crucifer
Arabidop-
sis thaliana
genome (Arabidopsis Genome Initia-
tive 2000), and subsequent work with the model
cereal rice (Delseny 2007), data are rapidly emerg-
ing on genes and genetic pathways related to a
number of developmental processes. The hope is
that the conservation of gene content and func-
tion from Arabidopsis, rice, and other cereals
would provide insight for understanding wheat
development. Indeed, it appears this hope has
been justifi ed in some instances and a generic
model has emerged for some processes and traits.
Efforts are underway to transform data from
molecular biology into information and under-
standing on the physiological level. Unfortu-
nately, linkage of molecular biology with many
developmental processes has not been well estab-
lished. Considerable challenges remain for under-
standing and characterizing the function of a
gene, identifying the complex genetic pathways
for a process, and determining the environmental
effects on gene expression before integration
with breeding and whole-plant physiology is
successful (Edmeades et al., 2004; White et al.,
2004a,b).
One area of notable success has been the eluci-
dation of the genetic controls of the fl owering
pathway (e.g., Hay and Ellis 1998; Laurie et al.,
2004 for barley; Beales et al., 2007), and most
recent understanding gained for wheat is thor-
oughly discussed in Chapter 3. Functional ortho-
logues of many of the genes involved have been
identifi ed between Arabidopsis, rice, wheat,
