Ram C. Yadav

MYB transcription factor genes as regulators for plant responses: an overview

Regulation of gene expression at the level of transcription controls many crucial biological processes. Transcription factors (TFs) play a great role in controlling cellular processes and MYB TF family is large and involved in controlling various processes like responses to biotic and abiotic stresses, development, differentiation, metabolism, defense etc. Here, we review MYB TFs with particular emphasis on their role in controlling different biological processes. This will provide valuable insights in understanding regulatory networks and associated functions to develop strategies for crop improvement.

High frequency plant regeneration from desiccated calli of indica rice (Oryza Sativa l.)

An efficient and reproducible protocol is required to achieve high frequency transformation from transformed calli. We report here high frequency plant regeneration from mature seed derived embryogenic calli of two recalcitrant indica rice cultivars HKR-46 and HKR-126 after partial desiccation treatment. Embryogenic and nodular callus was initiated on MS basal medium supplemented with 2.5 mg l -1 2,4-D, 500 mg l -1 proline, 500 mg l -1 casein hydrolysate, 30 g l -1 sucrose and 2.5 g l -1 gelrite. Several media with different combinations of growth regulators were tried. Maximum shoot regeneration frequency (63%) was observed in partially desiccated calli for 48 h in cv. HKR 46 and 82.1 per cent in cv. HKR-126 on the MS modified medium supplemented with 2 mg l -1 kinetin + 0.5 mg l -1 NAA + 30 gl -1 sucrose + 6 g l -1 gelrite followed by in the medium supplemented with 1 mgl -1 2ip + 30 g l -1 sucrose + 6 g l -1 gelrite (61% in cv. HKR-46 and 79.2 % in cv. HKR-126). Highly significant regeneration differences were observed in partially desiccated calli (48 h) in comparison to non-dehydrated (0 h desiccation) calli. Shoot regeneration frequency increased from 1.2 to 5.6 fold after 48 h of desiccation in both the cultivars on different regeneration media. Shoot regeneration frequency declined at 72 h desiccation treatment as compared to 48 h treatment. Well-developed plantlets were hardened and transferred to the green house. Key words: Plant regeneration; indica rice; mature embryo; partial desiccation. African Journal of Biotechnology Vol.3(5) 2004: 256-259

Sequence-related amplified polymorphism (SRAP) molecular marker system and its applications in crop improvement

Plant biotechnology has great potential for improving target traits in crops. This can be achieved by the production of transgenic crops and marker-assisted breeding. Marker-assisted breeding has gained momentum in recent times since it does not need biosafety regulations. Several kind of molecular markers are available for use in crop breeding, such as restriction fragment length polymorphism, microsatellites, sequence characterized amplified region, sequence-tagged site, inter-simple sequence repeat amplification, amplified fragment length polymorphism and single nucleotide polymorphism. Sequence-related amplified polymorphism is a novel molecular marker system which is based on open reading frames (ORFs) developed from genome sequence data of Arabidopsis. It provides a unique combination of forward and reverse primers which can be selected arbitrarily giving a large number of primer combinations. Since this is an ORF-based marker system, it targets functional genes and has potential for their application in crop breeding. This marker system was first used and demonstrated by Li and Quiros in Brassica oleracea in 2001, and since then there have been several reports in different plant species ranging from field crops to tree species for assessing genetic diversity, mapping and tagging of genes, hybrid identification and sex determination. This review provides an overview of SRAP markers and their applications in crop improvement.

Genetic Engineering for Tolerance to Climate Change-Related Traits

Climate change is expected to introduce new challenges for sustainable crop production worldwide. High temperature, less water availability, and emergence of new pests and pathogens calls for changing strategies and using biotechnological interventions to meet these challenges to sustaining food supply. Engineering biotic and abiotic stress tolerance will require concerted and combined efforts by plant breeders and biotechnologists alike. Several genes have been identified to have potential in mitigating climate change effects. These can be broadly classified as single-action genes and multiple action genes. Single action genes include osmoprotectants, detoxifying, LEA, HSP, ANPs, and ion transporters which have incremental roles in providing abiotic stress tolerance. Multiaction regulatory genes provide an attractive strategy to improve crop plants as these genes activate a cascade of genes which act together to enhance stress tolerance. CBF/DREB, SNAC, MYB, HSF, and AREB are some candidate genes of this category. Signal transduction genes such as osmosensors, AHK1, SNF1-related kinases are potential candidate genes for engineering stress tolerance in the near future. For insect resistance cry genes will remain the ideal choice however, engineering biotic resistance will involve new technologies such as RNAi and micro RNAs for combating insects and pests. Regulatory genes and genes involved in signal transduction will assume great importance in developing cultivars adapted to the threats of climate change. Here we review the target traits and potential genes for engineering stress tolerance in crop plants to meet climate change challenges for food production.

Engineering Abiotic Stress Tolerance Traits for Mitigating Climate Change

Crop yield, survival, and biomass production are negatively influenced by abiotic stresses. Due to multigenic nature, the molecular basis of abiotic stress tolerance is difficult to understand. Modern agriculture faces various challenges which include global climate change, complex field environment, and the combination of abiotic stress. To improve abiotic tolerance in crop plants, a combined effect of various molecular and biochemical approaches will be needed. Advanced molecular biology tools are used to enlighten the regulation mechanism of abiotic stress tolerance based on expression analysis of various stress-linked genes. The data collected from high-throughput transcription profiling, identification of specific protein network on large scale, molecular modeling and their association with environmental changes in plants all reveal information about plant system which is used for engineering plants against various environmental changes. Various genes for abiotic stress tolerance in crop plants have been identified and cloned to develop stress tolerant plants. In spite of various advancements in the technology, the success in developing stress tolerant plants is limited. This review enlightens the recent advancement in transgenic technology for the betterment of crop plants against abiotic stress.

A comparative genetic diversity analysis in mungbean (Vigna radiata L.) using inter-simple sequence repeat (ISSR) and amplified fragment length polymorphism (AFLP)

Amplified fragment length polymorphism (AFLP) and inter-simple sequence repeat (ISSR) markers were used to study the DNA polymorphism in elite mungbean genotypes. A total of nine AFLP primer combination and 22 ISSR primers were used. Amplification of genomic DNA of the 30 genotypes, using AFLP analysis, yielded 300 fragments that could be scored, of which 192 were polymorphic, with an average of 21.3 polymorphic fragments per primer. Number of amplified fragments with AFLP primers ranged from 29 (E-AAC: M-CAG) to 10 (E-ACG: M-CAT). Percentage polymorphism ranged from 46.3% (E-AAC: M-CCA) to a maximum of 100% (E-AAC: M-CAC), with an average of 64%. The 22 ISSR primers used in the study produced 108 bands across 30 genotypes, of which 68 were polymorphic. The number of amplified bands varied from two UBC820) to ten URP 6F). The average numbers of bands per primer and polymorphic bands per primer were 4.9 and 3.1, respectively. Percentage polymorphism ranged from 25% (UBC844) to 85% (UBC846, UBC864, UBC895), with an average percentage polymorphism of 58.3% across all the genotypes. AFLP markers were more efficient than the ISSR assay, as they detected 64% polymorphic DNA markers in Vigna radiata as compared to 58.3% for ISSR markers. The Mantel test between the two Jaccards similarity matrices gave r = 0.19, showing low correlation between AFLP- and ISSR-based similarities. Clustering of genotypes within groups was not similar when AFLP and ISSR derived dendrograms were compared. Key words : AFLP, ISSR, Vigna radiata (mung bean), marker index, unweighted pair-group method with arithmetic averages (UPGMA).