Page 7 - Genomics and Applied Biology

Genomics and Applied Biology, 2011, Vol.2 No.2
http://gab.sophiapublisher.com
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Figure 3 Comparative amino acid sequence analysis of the two cytochrome genes isolated from resistant (FJ712209) and (FJ712210)
sensitive tomato cultivars (TY70/84 and TY20) respectively
Note: Conserved substitutions are designated by (:); Semiconserved substitutions are designated by (.)
controlled. The obtained transcripts of the PR-proteins
(PR-1.1 and PR- 1.2) exhibited a rapid
up-regulation as early as 4 days post-inoculation,
reaching maximum levels after 16 days, followed by
down-regulation after 32 days. Conversely, maximum
expression of the Chitinase A gene (ChiA) and the
Gluconase (Glu-3) was observed following 16 and 32
days post-inoculation, respectively.
There is a close relationship among the upregulated
genes, ALY family genes, and P19 expression on the
resistant tomato cultivars. The expression of P19 was
low when amplified from the sensitive tomato cultivar
TY20. Cytochrome genes and ALY family genes in
the resistant cultivars did not mutate but they went
through a mutation in the sensitive cultivar, which
insures that viral P19 makes silencing for both
cytochrome and ALY family genes in the sensitive
cultivar. Moreover, many down-regulation genes were
observed in the sensitive cultivar, especially when
examined by primer H3FH. P19 is responsible for
silencing the plant defensin genes during the viral infection
(Omarov et al., 2006). The same observation was
brought up by Qiu et al (2002), who postulated that
P19 must be expressed early during virus infection
and at high levels. Lakatos et al (2004) demonstrated
that RNA silencing spreads through the vascular tissue
from the place of initiation to distant parts of the plant,
and sequestration of siRNAs by P19 may block the
spread of a systemic silencing signal.
1.3 Sequence and sequence analysis for the up- and
down- regulated genes
Sequence analysis revealed that the first two upregulated
genes were cytochrome oxidase subunit one with
identity 46%. But the other four genes showed identity
with the ALY-family genes with similarity 66%. The
obtained ALY-family genes showed similarity only
with those of Nicotiana benthamiana. Virus infection-
induced host gene down regulation have been
investigated mainly in cotyledonary and embryonic tissues
(Escaler et al., 2000; Havelda et al., 2003). Phylogenetic
construction based on nucleotide sequence of cytochrome
gene was compared with 18 different cytochrome genes
of different organisms. The neighbor- joining distance
analysis with maximum sequence difference of 0.75
and the topology showed two distinct lineages
including the 18 cytochrome genes. This lineage was
divided into two groups. The maximum nucleotide
sequence divergence was exhibited in lineage I. Meanwhile,
the obtained cytochrome genes appeared in the 2 nd
lineage as monophyletic sister clade (Figure 4). P19
interacts with plant ALY proteins and relocalizes a subset
of these proteins from the nucleus to the cytoplasm (Canto
et al., 2006). It could be concluded that the cytochrome
oxidase produced in cytoplasm by mitochondria helps
the cell to control the movement of the viral particles
from cell to cell and also to resist the RNA silencing
activity of the viral P19 gene (Canto et al., 2006). In
spite of the fact that the mitochondrial cytochrome
oxidase C is a highly conserved electron transport
protein coded by multiple genes containing regions
that evolve at different rates (Lunt et al., 1996), it is
considered as a defense system against the biotic and
abiotic stresses. Maas & Sanjur (1996) reported partial
cytochrome oxidase subunit I (COI) DNA sequences
for S. frugiperda strains further substantiating mtDNA