Agriculture Reference
In-Depth Information
isoenzyme GS1-3 plays a major role in controlling kernel yield [159];
Figure 3). The hypothesis that GS is one of the key steps in the control
of cereal productivity was strengthened by a study performed on rice, in
which a co-localization of a QTL for the
GS1;1
locus and a QTL for one-
spikelet weight was identifi ed [183]. As a confi rmation, a strong reduc-
tion in growth rate and grain yield was observed in rice GS1;1 defi cient
mutants [184].
The role of the GS enzyme and other N-related physiological traits in
the control of agronomic performance in wheat still remains to be clearly
established. Using a quantitative genetics approach, Fontaine et al. [185]
found only a co-localization between a QTL for GS activity and
GSe
, a
structural gene encoding cytosolic GS, but no obvious colocalization with
a QTL for yield, in agreement with previous work published by Habash
et al. [158]. In contrast, in recent work, physical mapping, sequencing,
annotation and candidate gene validation of an NUE QTL on wheat chro-
mosome 3B suggested that the NADH-dependent GOGAT enzymes con-
tribute to NUE in wheat and other cereals [186] in agreement with work
previously performed on rice [167].
Interestingly, in a woody species such as maritime pine that is far away
from cereals on an evolutionary point of view, a protein QTL for GS co-lo-
calized with a GS gene and a QTL for biomass [187]. Functional validation
of the pine GS gene in transgenic poplars (see above), which can be con-
sidered as a crop for wood production, shows once again that quantitative
genetics represent one of the most powerful approaches for identifying NUE
candidate genes that may be involved in the control of plant productivity.
To date, there are only a few reports reporting specifi c breeding for
organic input systems and especially N [188]. A question that could be
addressed is whether the genetic control of NUE under organic or con-
ventional fertilization conditions is similar or if there are specifi c genes or
combinations of genes that are more adapted to one mode of fertilization
compared to the other, taking into account that organic material can be
directly taken up by the plant [189]. Moreover its appears that using ap-
propriate selection environments is important for breeding crops adapted
to organic farming systems [190].
Further work is necessary to identify whether other root and shoot en-
zymes or regulatory proteins could play a specifi c role under low or high
