Agriculture Reference
In-Depth Information
a putative amino-terminal signaling domain, a nucleotide binding site and a series
of carboxy-terminal leucine repeats (Meyers et al.
2005
). Two different types of
NBS-LRR proteins have been reported. One major class has an amino-terminal
TIR (Toll/interleukin receptor) domain also called TIR-NBS-LRR or TNL proteins.
Other class includes the genes which encode an amino-terminal coiled-coiled motif
(CC-NBS-LRR or CNL proteins). The mechanism of resistance induced by
Pm3a
and its other allelic forms in wheat (Feng et al.
2010
) and by
Pb1
against rice blast
clearly exemplifies that the single amino acid residue at the final position of the ki-
nase-2 motif is the characteristic of coiled-coil (CC) motif while the trytophan (W)
and aspartic acid (D) are the characteristics of TIR-type proteins. The details of the
molecular functions of these protein domains and their interacting partners are still
being established. However, the consistent identification of this class of proteins
across diverse plant species demonstrates that the NBS-LRR genes are a pillar of
plant defense against pathogen. The majority of the
R
genes in
Arabidopsis
are TNL
genes; however they have not yet been reported in cereals. In rice, about 1,500 NBS
coding sequences were analyzed and not a single sequence was known to have TIR
binding domain (Zhou et al.
2004
).Three leaf rust resistance genes,
Lr1, Lr10, Lr21
and one powdery mildew resistance gene,
Pmb3b
, are known to have CNL type
domain (Feuillet et al.
2003
; Huang et al.
2003
; Yahiaoui et al.
2004
).
Conclusions and Future Prospects
Three areas of prevailing concern that have received enormous attention are global
warming, climate change and food security. Associated with these has been popula-
tion growth with futuristic projections made first at 2025 (8.2 billion) and now for
2050 at 9.2 billion expected to touch 10 billion swiftly by 2055. The three catchy
buzz words above have generated many discussion fora, created a lot of debate and
delivered numerous “smart” ideas as the outcome of various interactive sessions.
However, at the end of the day if we look at national “wheat” based food security
it is doubtful if we are better off now in 2012 than we were a few years before. Our
productivity is not that earth shaking, average national yields in several countries
fluctuate yearly and the yield gap remains as significant as before. The stress con-
straints are more complex and the resolve to adopt a way forward for achieving
promising returns rather feeble. Have we addressed these constraints and can the
outputs be quantified? The trend is negative or on the conservative side “STATIC”
as to progress. The umbrella cover that integrates research/production activities is
non-existent and resources are far from being neatly agglomerated. Taking wheat
in Pakistan as an example we still hover around 25 million tons per acre and mean
yields are not beyond 25-30 maunds. The per hectare figure is estimated at 2.6 t.
Stress constraints still dominate the scene and one wonders if solutions have been
found to allow us to see durability with high value. Problems galore relate to the
three rusts with stem rust the one abused most for personal projection and profes-
sional clout but done with questionable structural quality science. Then come other
Search WWH ::
Custom Search