فصلنامه ژنتیک نوین
سال چهارم شماره 4 (پیاپی 19، زمستان 1388)

Legumes are important crop plants as human and animal feeds. They are able to establishnitrogen-fixing symbiosis with soil rhizobia and also to form symbiotic root mycorrhizae. Thesoilborne pathogen Ralstonia solanacearum is the causal agent of bacterial wilt and attacks more than 200 plant species, including some legumes. This pathogen blocks the plant vessels and also can digest the plant key enzymes via secretion system type III resulting in plant death. In this study, the resistant and susceptible Medicago truncatula were used as model plants to investigate the gene expression changes against R. solanacearum. The proteomics and transcriptomics studies showed that the expression of two groups of genes increases in both resistant and susceptible plants against R. solanacearum. The first group, including the product of resistance genes such as PI, PR and peroxidase proteins interacts with pathogen directly. The second group is genes that play as transcription factors, signal transduction or chaperon like proteins such as HSP90 and peptidyl-prolyl cis-trans isomerase (PPI). The transcriptomics studies showed that the induction of gene expression in the resistant plants were stable but transient in the susceptible plants. One day after bacterial inoculation, the genes expression were induced in both resistant and susceptible plants but reduced in susceptible plants in day three post inoculation.

The extra genetic progress by using DNA information indicated that the genetic merit canenhance through increasing the accuracy of genetic evaluations across a population. This study investigated whether selection using genetic markers linked to quantitative trait loci (QTL) increased selection accuracy of potential young bulls for progeny testing experiment in marker-assisted selection (MAS) breeding scheme. Besides, the effect of selective genotyping in potential bulls as candidates for progeny testing on the accuracy of total estimated breeding values was studied based on stochastic simulation of a population resembling a commercial dairy cattle breeding scheme for 25 yr. Two levels of selective genotyping (20 and 50%) were performed to sample young bulls compared toeither complete genotyping (100%) or no genotyping (0%) of potential candidates. A trait with low heritability (h2=0.04) only expressed in females was used. One bi-allelic QTL with 25% of the genetic variance and 4 markers were simulated in an identified 4cM region of a chromosome in linkage disequilibrium. Using marker information in selection schemes indicated that the accuracies among the potential candidates were higher than conventional evaluations without including genotype information.In comparison to complete genotyping of young bulls during years 6-11, the superiority of using QTL information were 76-82% with 50% genotyping, 51-67% with 20% genotyping, and 46-55% using conventional prediction methods. Lower accuracies were appeared in using genotypic information where favorable QTL allele was closed to fixation. Therefore, using a detected-QTL and selective genotyping during the young ages to identify the proper candidates (young bulls) can be considered as an efficient method to improve the selection accuracy with lower genotyping costs.

In order to study the relationships among components of resistance to yellow rust (Puccinia striiformis f.sp. tritici), 47 wheat genotypes of national plant gene bank of Iran were assessed by 4 pathotypes of 6E6A+, 134E134A+, 134E142A+ and 6E4A+ at seedling stage. Correlation Analysis among components of resistance showed that association between latent period and pustule density was not influenced by the pathotype but relationship between latent period and pustule size was affected bythe pathotype of the pathogen. Principal component analysis based on components of resistance, for each pathotype separately, indicated that latent period have the largest effect on the variation of relating principal components. Principal component analysis based on components of resistance for all pathotypes showed that the first 4 components justified 81% of the total variation in the data. Coefficients of traits revealed that the first principal component indicates susceptibility to all pathotypes and the second principal component indicates specific resistance to pathotypes of 134E134A+ and 6E4A+ and sensitivity to pathotypes of 6E6A+ and 134E142A+. Studied genotypes were divided into two groups of resistant and susceptible by cluster analysis through UPGMA method based on principal components. The results of this investigation demonstrated that latent period could be a suitable replacement for other components of resistance to yellow rust in order to select superior genotypes.

In order to compare two linear-linear (LLM) and linear-threshold (LTM) models for estimation of genetic and environmental parameters, a population consisting of 6,700 animals was simulated using the Visual Basic programming language. The heritabilities for the first and second trait were assumed to be 0.30 and 0.10, respectively, and the genetic correlation between two traits was 0.50. Selection of parents was based on a two-trait selection index, and mating of selected parents conducted randomly for 15 years. The second trait was transformed into a categorical trait, assigning 50% ofobserved data in the first category, 34% in the second, and 16% in the third, using the probit function. In the LLM, genetic and environmental parameters were estimated under animal model specifications and derivative free restricted maximum likelihood methodology. In the LTM, predicted breeding values were obtained using a Bayesian method, implemented via Gibbs sampling procedure. The two models showed high ability in estimating genetic and environmental parameters for the continuous trait, and results were similar. Estimated genetic parameters for the threshold trait in LTM were higher than LLM, as the estimate of additive genetic variance and heritability was higher in LTM (0.084 and 0.10) than in the LLM (0.035 and 0.07) for the threshold trait. Therefore, the LTM offered advantages over the LLM in estimation of genetic and environment parameters, specifically in categorical trait) but due to a wide range of traits’ heritabilities and correlation between them under natural situation, further researchs usingfield data and other parameters are required.

Freezing tolerance will be induced in most of the plants when they expose to non-freezingtemperatures. This process is called cold hardening. Several studies showed that, expression of cold regulated genes in plants is necessary for cold tolerance and hardening. In present study, expression pattern of a differentially expressed gene under cold hardening belonged to sugar transporter group (SuT4) was investigated in freezing susceptible and tolerant varieties of wheat. Additional study was performed on 5'-upstream region (promoter) of this gene. 4ºC was used to induced hardening treatment on 2- weeks old seedling. Sampling was carried out before and after hardening treatment.Quantitative real-time PCR approach was used to evaluate gene expression pattern using SYBR Green dye. The sequence of promoter region of gene was isolated and evaluated by genome walking based on PCR and PlantCARE and PLACE softwares Based on the results, SuT4 was up-regulated significantly in first day after hardening in both variety compared to non-treated plants but its expression was higher in tolerant variety than susceptible one over the experiment. The gene has promoter with 1980 bp and without TATA and CAAT box. The promoter contained many putative cis-acting regulatory elements, including abscisic acid (ABA)- responsive element, dehydration-responsive element, low-temperature responsive element and many other regulatory elements. Because of the expression of SuT4 was increased significantly in both variety, this gene may has been a role only in cell adaptation under stress condition or has a dual role to control cold stress and snow mold resistance.

Gene therapy using gene targeting approach is one of the best therapeutic methods for treatment of monogenic disorders. In contrast to application of viral vectors, gene targeting has low efficiency. The scope of this study is to design and construct a lentiviral vector without integration into the genome, but entering into the cell nucleus with high efficiency. In this study after transduction of 293T cells with native virus and recombinant virus, eGFP percentage in transduced cells with native virus was decreased slightly two weeks after viral treatment. In contrast, in negative integrase viruses a dramatic decrease was observed. Results shows that recombinant virus genome remains as episomal and integrates with lower efficiency into the host genome which has the lowest undesired effect on expression of other genes of cell. Defective gene can be replaced by gene entered into the cell nucleus without any viral genome portion integration into the host genome.

this study examines the hypothesis that antioxidant enzymes are involved in alleviating theoxidative damage on plant developmental process on generative stage caused by an increase in reactive oxygen species under water stress. Therefore, effect of water stress on the enzyme activity of ascorbate peroxidase (APX), catalase (CAT), peroxidase (POX) and superoxide dismutase (SOD) were analyzed by spectrometric and gel assay procedures at generation stages of barley (5 stages) in field condition. The experiment was conducted according to randomized complete block design with three replications and was analyzed on the complete factorial (3 different stress × 5 developmental stages× 5 genotypes). According to the variance analysis, all simple and interaction effects have significantly difference in almost all traits. The amount of total protein and chlorophyll content were significantlydeclined with the progress of plant growth. Activities of all enzymes were increased in initial growth stages and decreased in later growth stages. The reduction of activities was significantly high, while these activities had no intensive difference with the initial stages. In general, activity of antioxidant enzymes was increased compared to high reduction of total protein content in the cell. In such condition, both APX and CAT showed a high level of expression to protect the cells from oxidative damage especially at drought stress and dry farming conditions. Kinetic assays were confirmed by isozymic analysis using gel assay. From the results of this investigation, it can be concluded that the studied antioxidant enzymes may have a role to protect plant cells from active oxygen species caused by drought stress at the dry farming condition.Antioxidant enzymes, Senescence, Water stress, Barley, Growth stages.