Agriculture Reference
In-Depth Information
plant's total nitrogen content, is left to replenish the soil's nitrogen content
(Khan
et al
. 2003; Mahieu
et al
. 2007; McNeill and Fillery 2008).
S
OYBEAN AS A
M
ODEL
S
PECIES TO
I
MPROVE
L
EGUME
C
ROP
P
RODUCTIVITY
Due to its economic relevance, a great deal of research has been dedicated
to soybean in an effort to identify unique traits / cultivars that produce superior
growth characteristics and yields. As a result, soybean has been at the forefront
of some of the most significant advances in modern-day agronomy. Perhaps
most notably occurred in 1996 when commercial production of genetically
engineered soybean began in the USA. Today, the majority of soybean grown
in the USA is genetically-engineered, making it the world's first large-scale
commercial transgenic crop.
For research purposes, soybean also represents an excellent model plant
for understanding other valuable legume species (Ferguson and Gresshoff
2009). This includes, but is not limited to, chickpea, bean, pea, lentil, lucerne,
peanut, lupin and clover. In fact, soybean and pea (
Pisum sativum
) have been
the most widely used model species to study legume physiology for over a
century. As a result, these two species have provided tremendous insight into
the growth and development of legumes, with outcomes being extrapolated to
the other less-researched legumes.
In more recent years, there was a shift away from using soybean and pea
as the main model legume species. This can be attributed to an overall shift in
plant science, which switched from being predominantly physiology-based to
having a more molecular focus. As a result, there was a need for legume
species having relatively small and easily manipulated genomes; two traits that
soybean and pea did not offer. Thus, despite having almost no economic
relevance, the legumes
Lotus japonicus
and
Medicago truncatula
were quickly
adopted as the modern-day model legume species in place of soybean and pea,
respectively. Indeed,
L. japonicus
and
M. truncatula
met the requirements of
having small genomes and were regarded as the most efficient and effective
species for identifying novel legume genes. Outcomes using these two
‗modern' model legumes could subsequently be transferred to more
economically significant species via comparative genomics, etc. This approach
was highly successful. As a result, a great deal of what we currently know
about the genes and signals involved in legume nodulation can be directly
