Mining of Candidate Maize Genes for Nitrogen Use Efficiency by Integrating Gene Expression and QTL Data

Breeding maize varieties for high nitrogen (N) use efficiency (NUE) by marker-assisted selection using NUE quantitative trait locus (QTL) or by genetic transfer of NUE-associated genes is a viable approach for increasing grain yield in N-limited production areas. In this investigation, we evaluated a set of introgression line populations under N supply and N deficiency conditions. From 42 QTLs for grain yield and yield components, 23 were identified under N supply conditions and 33 from N limited conditions. Meta-analysis of published maize NUE QTLs revealed 37 “consensus” QTLs, of which, 18 was detected under low N conditions. In addition, 258 unique ESTs associated with low N stress response, N uptake, transport, and assimilation were aligned on the maize genome by in silico mapping. Integrating the EST map with the QTL map has resulted in the identification of candidate NUE-associated genes of the following functional categories: N uptake, transport, and assimilation; carbon (C) metabolism and assimilation; and cascades of stress response and signal transduction genes. Nine candidates that have been introgressed into Ye478 significantly altered grain yield/yield components. It is suggested that the dynamics of interactions between C and N metabolism are important for maize yield. A high NUE variety should have a highly efficient C assimilation per unit N and actively express CO₂ assimilation-related genes under N-limited conditions.     

Generation and analysis of drought stressed subtracted expressed sequence tags from safflower (Carthamus tinctorius L.)

Drought is the most crucial environmental factor that limits productivity of many crop plants. Exploring novel genes and gene combinations is of primary importance in plant drought tolerance research. Stress tolerant genotypes/species are known to express novel stress responsive genes with unique functional significance. Hence, identification and characterization of stress responsive genes from these tolerant species might be a reliable option to engineer the drought tolerance. Safflower has been found to be a relatively drought tolerant crop and thus, it has been the choice of study to characterize the genes expressed under drought stress. In the present study, we have evaluated differential drought tolerance of two cultivars of safflower namely, A1 and Nira using selective physiological marker traits and we have identified cultivar A1 as relatively drought tolerant. To identify the drought responsive genes, we have constructed a stress subtracted cDNA library from cultivar A1 following subtractive hybridization. Analysis of?~1,300 cDNA clones resulted in the identification of 667 unique drought responsive ESTs. Protein homology search revealed that 521 (78?%) out of 667 ESTs showed significant similarity to known sequences in the database and majority of them previously identified as drought stress-related genes and were found to be involved in a variety of cellular functions ranging from stress perception to cellular protection. Remaining 146 (22?%) ESTs were not homologous to known sequences in the database and therefore, they were considered to be unique and novel drought responsive genes of safflower. Since safflower is a stress-adapted oil-seed crop this observation has great relevance. In addition, to validate the differential expression of the identified genes, expression profiles of selected clones were analyzed using dot blot (reverse northern), and northern blot analysis. We showed that these clones were differentially expressed under different abiotic stress conditions. The implications of the analyzed genes in abiotic stress tolerance are discussed in our study.     

Identification and annotation of abiotic stress responsive candidate genes in peanut ESTs

Peanut (Arachis hypogaea L.) ranks fifth among the world oil crops and is widely grown in India and neighbouring countries. Due to its large and unknown genome size, studies on genomics and genetic modification of peanut are still scanty as compared to other model crops like Arabidopsis, rice, cotton and soybean. Because of its favourable cultivation in semi-arid regions, study on abiotic stress responsive genes and its regulation in peanut is very much important. Therefore, we aim to identify and annotate the abiotic stress responsive candidate genes in peanut ESTs. Expression data of drought stress responsive corresponding genes and EST sequences were screened from dot blot experiments shown as heat maps and supplementary tables, respectively as reported by Govind et al. (2009). Some of the screened genes having no information about their ESTs in above mentioned supplementary tables were retrieved from NCBI. A phylogenetic analysis was performed to find a group of utmost similar ESTs for each selected gene. Individual EST of the said group were further searched in peanut ESTs (1,78,490 whole EST sequences) using stand alone BLAST. For the prediction as well as annotation of abiotic stress responsive selected genes, various tools (like Vec-Screen, Repeat Masker, EST-Trimmer, DNA Baser, WISE2 and I-TASSER) were used. Here we report the predicted result of Contigs, domain as well as 3D structure for HSP 17.3KDa protein, DnaJ protein and Type 2 Metallothionein protein.     

植物适应土壤氮素环境的基因选择:以水稻为例

在农业生产过程中,施用无机氮肥是提高作物产量的基础,但氮肥过量施加对生态系统和植物发育进程均会产生不利影响。因此,提高作物氮素利用效率是农业可持续发展的关键。目前,对重要粮食作物水稻(Oryza sativa)的氮高效研究取得了一系列重要进展,并克隆到多个调控氮素吸收、转运和代谢的关键基因。然而,在不断被人工选育的过程...