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Articles by K. Nadarajah
Total Records ( 6 ) for K. Nadarajah
  K. Nadarajah , N.M. Kasim and V.V. Fui
  In this study, we describe the gene that codes for MAPK in Oryza rufipogon and Oryza sativa that reacts towards the blast disease (causative agent is Magnaporthe grisea) and brown planthoppers (Nilaparvata lugens). This gene has been isolated and characterized in Oryza sativa and in this study the same gene has been isolated from Oryza rufipogon using OsMKK1 as a template and named OrMKK1. Through conducting this study, we found that Oryza rufipogon contains two copies of the MAPK gene in its genome. A comparative study was conducted between OrMKK1 and OsMKK1; and the results showed that both these genes responded towards biotic stress. Though both the genes share a high level of amino acid similarities (94%), the kinetic reactions of both genes are different.
  K. Nadarajah , C.Y. Choong , S.J. Leong and R. Wickneswari
  Calamus manan floral cDNA libraries were constructed for four stages of flowering in male and female plants, respectively. The Calamus manan inflorescence ESTs were generated to provided a better understanding of the flowering process through the identification of genes that are expressed in the floral tissues of this plant. The BLASTX homology search showed that 119 ESTs that were generated from this study had significant matches to unknown proteins and an additional 127 ESTs did not match any protein sequences in the NCBI database. Therefore, a motif search was carried out for the unknown ESTs to predict their putative functions. A total of 136 EST clusters were used in the motif analysis and the InterProScan software was chosen as the motif search tool. There were 66 types of motifs detected from this search. Based on the motifs detected within the query sequences, putative function predictions were successfully performed on 49 EST clusters.
  K. Nadarajah , N.M. Kasim and V.V. Fui
  The effect of salinity, wounding and drought on the expression of a MAPK gene in rice was analyzed in this research. OrMKK2, an ortholog of the Oryza sativa japonica OsMAP1 (OsMPK5), was isolated and characterized in this study. This gene is 1381 bp long and has a 5’UTR that is 120 bp and a 3’UTR that is 195 bp and it encodes a protein that is 356 amino acids long. When analyzed against a previously isolated OrMKK1, the gene exhibited similarities in the 11 domain locations and showed 96% identity to OrMKK1. Unlike OrMKK1, the OrMKK2 gene contained two copies of the gene in the genome. OrMKK2 appeared to be positively regulated by abiotic stress.
  K. Nadarajah and N.M. Kassim
  A putative protein kinase gene was isolated from Oryza rufipogon using the OsMKK1 as template for primer synthesis. This gene was used to analyse the involvement of signal molecules and hormones in signal transduction of mitogen-activated protein kinase. The 352 amino acids long MAPK has a molecular weight of 37 kDa and a pI value of 6.1. The gene sequence contained a dual-phosphorylation activation motif TDY (Thr-Asp-Tyr) and four activity domains (catalytic loop, activation loop, ATP binding site and substrate binding site). The 5’UTR of the gene was also analysed and was shown to contain the MYBCORE, ERE, GT-1 and GATA box, all of which have a role to play in MAPK function. Here we have treated the OrMKK1 lines with Jasmonic Acid (JA), salicylic acid (SA), ethylene (ET), benzothiadiazole (BTH) and abscisic acid (ABA) to determine the involvement of these molecules and hormones in MAPK signal transduction. OrMKK1 gene was induced by JA, SA, BTH and ET but was delayed and weak in ABA. The highest level of expression is seen in JA treated plants. The transcript level of this gene was also studied in various tissues and organs of rice and the results show that the gene is developmentally regulated as clearly seen from the Northern analysis conducted on rice tissues. The results from this study suggest that OrMKK1 may be activated by signal molecules and hormones and this gene may play a role in the plant defense mechanism.
  K. Nadarajah , J. Kader , Mohd. Mazmira and D.C.Paul
  In this study chitosan was extracted from the mycelia of Rhizopus sp KN01, Rhizopus sp KN02, Mucor sp KN03 and Aspergillus niger with the highest amount of extractable chitosan obtained at the late exponential phase. The amount of chitosan produced varied widely amongst isolates. Mucor sp KN03 produced the highest amount of extractable chitosan per ml of substrate and the highest yield of chitosan per unit mycelia mass.
  K. Nadarajah , N.M. Hanafi and S.L. Tan
  Coat protein (CP), Movement Protein (MP) and Overlapping (OVG) genes were isolated from a Malaysian Cucumber mosaic virus (CMV) isolate via RT-PCR and transformed into Nicotiana tabacum through Agrobacterium tumefaciens-mediated transformation. Out of the thirty six independently transformed lines developed from the three different genes and the mutants of MP and OVG, five lines were tested for resistance against CMV by challenge inoculations using three different concentrations (1:10, 3:10 and 5:10) of CMV macerated in 0.1 M sodium phosphate buffer (pH 7.0). The transgenic lines exhibiting complete resistance remained symptomless even when re-inoculated with 1:10 concentration of virus. The level of viral RNA accumulation in inoculated leaves was significantly (at least 2-3 times) lower compared to the control untransformed plants. The upper leaves which were analysed for systemic spread of the infection had much lower levels of viral RNA accumulation compared to the inoculated leaves. Amongst the three genes and two mutant lines that were generated in this study, we found that the CP and MP genes were able to provide a better level of resistance to the plants compared to the overlapping gene.
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