increase in the endogenous concentration of SA,
whereas this defense response is avoided in the
case of a compatible symbiont.
9.9 Strigolactones (SLs)
Strigolactones (SLs) are newly identified hor-
mones that regulate multiple aspects of plant
development, infection by parasitic weeds, and
mutualistic symbiosis in the root. The correlation
between SLs and nodulation was previously
investigated inM. sativaandP. sativum, both of
which form indeterminate nodules. In these
species, root nodulation is positively affected by
the treatment of the SLs (Soto et al. 2010 ; Foo
and Davies 2011 ; Foo et al. 2013 ). The role of
SLs was studied inL. japonicususing transgenic
lines silenced for carotenoid cleavage dioxy-
genase 7(LjCCD7), an ortholog of Arabidopsis
More Axillary Growth 3. Silencing ofLjCCD7is
expected to reduce strigolactone levels. In L.
japonicus, LjCCD7-silenced plants had 20 %
fewer nodules than controls, suggesting that SLs
have a slight positive effect on the formation of
determinate nodules (Liu et al. 2013 ).
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