Identification and characterization of resistance gene analogs (RGA) from castor (Ricinus communis L.) for Fusarium wilt
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Date
2012-05
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Navsari Agricultural University, Navsari
Abstract
One of the key approaches for disease prevention and control in castor
(Ricinus communis L.) is to develop a disease resistant variety; this can be
achieved through tagging of resistance genes. In this study, a total of two
putative resistance gene analogues (RGAs) have been isolated and
characterized from resistant castor genotype (SKP-84) using primers targeted
at the conserved motifs of the known R gene in the database. Homology and
% identity searches of the isolated RGA sequences with the NCBI GenBank
database showed that p6.4 had 89% identity to the disease resistance like
proteins in castor and 23 had 100% identity with I2C disease resistant proteins
in tomato. Phylogenetic analysis indicated that the RGAs clustered with R
genes found in Arabidopsis and Tomato. The findings will be useful for
studying of resistance mechanism in castor to Fusarium. Induction of plant
defence against pathogen attack is regulated by a complex network of
different signals. Thus changes in various biochemical defences including
antioxidant enzymes, phenolic compounds andpathogenesis related (PR)
proteins were investigated the roots of resistant and susceptible genotypes of
castor at 0, 24, 48 and 72 h.a.i. by Fusarium oxysporium significantly
increased the SOD and POX activities in the roots of susceptible genotypes,
while the catalase activities were appreciably higher in the roots of resistant
genotypes at different stages. Constitutive levels of APX and PPO were
higher in the resistant genotypes. Also, activities of PAL and β 1, 3 glucanase
significantly increased in the roots of resistant genotypes after infections. Rate
of increment of MDA content was higher in resistant genotypes after
infection. Analysis of isozyme electrophoresis revealed that interaction
between plant and fungi invoked various isozymes at 48 hours of infection.
The isozyme banding pattern of SOD, POX, PPO and esterase were studied
during plant pathogen interaction and showed some induced isozymes.SOD 3
was observed only in resistant genotypes at 24 h.a. i . except ,
Geeta. Simi larly induction of POX 5 was observed only in resistant
genotypes at 48 hours of infection, though the intensity of POX 5 was very
less. Expression analysis of regulatory genes of ethylene and spermidine
biosynthesis using RT-PCR revealed higher expression of S-adenosyl
methionine decarboxylase, ACC Synthase and sepermidine synthase in the
roots of resistant genotypes at 4, 6 and 8 h.a.i., which shows role of ethylene
as signal molecule in disease resistance.These results reflect cascade of
signals activated by fungi which leading to the activation of defence system in
castor against wilt pathogen.
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Keywords
enzymes, planting, genes, diseases, biological phenomena, genotypes, proteins, castor (genus), fungi, vegetables