Role of RNA Interference in Pest Management 203
loss in the treated larvae as compared to control.
The above authors in the year 2013 further ex-
tended their studies and developed a new cotton
expressing dsRNA for both membrane perme-
ability enhancer gene 35S:GhCP1 and Cyto-
chrome 450 monoxygenease downregulationg
gene ( 35S:dsCYP6AE14). GhCP1 is the serine
protease of cotton that plays an important role
in plant-insect interactions. The entry of GhCP1
increases easier food absorption in the midgut.
To employ RNAi mediated protection in tob-
baco against H. armigera, Zhu et al. ( 2012 ) used
20-Hydroxyecdysone gene ( HaEcR), a steroid
hormone required for the growth and develop-
ment. In yet another study the ecdysone recep-
tor, EcR has been tested by engineering into the
tobacco which showed improved resistance to H.
armiger and Spodoptera exigua Hub.
In yet another study Zha et al. ( 2012 ) dem-
onstrated utility of RNAi in the management of
Nilaparvata lugens Stal by expressing dsRNA
for hexose transporter, trypsin like serine pro-
tease and carboxypeptidase. In this regard, the
above researchers identified RNAi core machin-
ery in N. lugens such as Nlsid-1 and Nlaub gene,
where Nlsid -1 is needed for the dsRNA uptake
and spread silencing signals among tissues.
By using virus-based expression of dsRNA in
plants, a new line of approach was developed in
RNAi mediated management of Manduca sexta
L. (Kumar et al. 2012 ). They called it as ‘plant
virus based dsRNA producing system’(VDPS).
It was originally described and used against
nematodes in the demonstration of the transient
RNAi response in tobacco plants using tobacco
rattle virus (Meyering-Vos and Muller A 2007 ;
Dubreuil et al. 2009 ). Kumar et al. ( 2012 ) em-
ployed nicotine detoxifying cyp genes which
were upregulated during nicotine detoxification,
particularly, CYP4B46, CYP4M1 and CYP4M3.
They selected the above three cyp targets based
on the sequence homology where CYP4B46
showed 85 % homology to CYP4B45, the other
two CYP4M1 and CYP4M3 showed 53 % simi-
larity. They transformed the entire fragment indi-
vidually into tobacco plants using VDPS meth-
od and CYP4B46 fragment alone transformed
into the plants using Agrobacterium mediated
transformation method. Interestingly this ap-
proach of silencing CYP4B46 did not affect lar-
val weight but the level of transcript, whereas,
the VDPS-CYP4M3 ingested larvae had gained
less weight as compared to control. In another
successful example, controlling H. armigera
was achieved by the knockdown of the hormone
regulating transcription factor HR-3 (Xiong
et al. 2013 ). The above authors studied the ef-
fect of dsRNA on the larvae by providing differ-
ent size fragments of dsRNAhaHR-3 delivered
through the artificial diet where the bacterially
expressed dsRNA could cause significant mortal-
ity in 3–7 days after treatment. Molecular vali-
dation of gene silencing showed that HaHR-3-1
and HaHR-3-3 were dominant in silencing effect
than HaHR-3-2 and HaHR-3-4, the repression of
this protein negatively affected the development
of the H. armigera.Imparting Plant Resistance to Viruses
Resistance to RNA viruses is brought about by
the enzyme RNA dependent RNA polymerase
sequence-specific degradation of the targeted
viral mRNA. Studies have indicated RNAi could
be brought about by siRNA or dsRNA molecules
that are cognate to the viral coat protein genes.
This has been demonstrated in tobacco, squash,
and papaya. But RNAi could not protect against
the infection of single-stranded DNA Gemini vi-
ruses that causes severe damage to cassava and
tomato (Auer and Frederick 2009 ).Bacterial Blight and Fungal Resistance
As compared to the other research areas appli-
cation of RNAi in offering protection against
fungal and bacterial pathogens is very scanty.
Some studies have indicated that small RNAs
have changed their expression during pathogen
attack and also regulate gene expression dur-
ing the pathogen attack. Take also participate in
regulation of gene expression involved in disease
resistance pathways. The small RNAs silence
the negative regulator molecules in the plant cell