Ambuj Bhushan Jha

Reactive Oxygen Species, Oxidative Damage, and Antioxidative Defense Mechanism in Plants under Stressful Conditions

Reactive oxygen species (ROS) are produced as a normal product of plant cellular metabolism. Various environmental stresses lead to excessive production of ROS causing progressive oxidative damage and ultimately cell death. Despite their destructive activity, they are well-described second messengers in a variety of cellular processes, including conferment of tolerance to various environmental stresses. Whether ROS would serve as signaling molecules or could cause oxidative damage to the tissues depends on the delicate equilibrium between ROS production, and their scavenging. Efficient scavenging of ROS produced during various environmental stresses requires the action of several nonenzymatic as well as enzymatic antioxidants present in the tissues. In this paper, we describe the generation, sites of production and role of ROS as messenger molecules as well as inducers of oxidative damage. Further, the antioxidative defense mechanisms operating in the cells for scavenging of ROS overproduced under various stressful conditions of the environment have been discussed in detail.

Gene‑based SNP discovery and genetic mapping in pea

Key messageGene-based SNPs were identified and mapped in pea using five recombinant inbred line populations segregating for traits of agronomic importance.AbstractPea (Pisum sativum L.) is one of the world’s oldest domesticated crops and has been a model system in plant biology and genetics since the work of Gregor Mendel. Pea is the second most widely grown pulse crop in the world following common bean. The importance of pea as a food crop is growing due to its combination of moderate protein concentration, slowly digestible starch, high dietary fiber concentration, and its richness in micronutrients; however, pea has lagged behind other major crops in harnessing recent advances in molecular biology, genomics and bioinformatics, partly due to its large genome size with a large proportion of repetitive sequence, and to the relatively limited investment in research in this crop globally. The objective of this research was the development of a genome-wide transcriptome-based pea single-nucleotide polymorphism (SNP) marker platform using next-generation sequencing technology. A total of 1,536 polymorphic SNP loci selected from over 20,000 non-redundant SNPs identified using deep transcriptome sequencing of eight diverse Pisum accessions were used for genotyping in five RIL populations using an Illumina GoldenGate assay. The first high-density pea SNP map defining all seven linkage groups was generated by integrating with previously published anchor markers. Syntenic relationships of this map with the model legume Medicago truncatula and lentil (Lens culinaris Medik.) maps were established. The genic SNP map establishes a foundation for future molecular breeding efforts by enabling both the identification and tracking of introgression of genomic regions harbouring QTLs related to agronomic and seed quality traits.

Allele diversity analysis to identify SNPs associated with ascochyta blight resistance in pea

Development of pea cultivars with improved resistance to ascochyta blight disease has been hindered due to lack of strong resistance. The objective of this study was to identify single nucleotide polymorphisms (SNPs) within the candidate genes associated with ascochyta blight resistance that can be used to aid selection. A total of 54 diverse Pisum sativum accessions from eastern Europe, western Europe, Australia, and Canada were genotyped and phenotyped for disease reaction. Fifteen SNPs were detected within candidate genes associated with reaction to ascochyta blight, of which SNP loci PsDof1p308 and RGA-G3Ap103 had significant associations with ascochyta blight scores. Further, PsDof1p308 showed significant association with disease score when tested on a recombinant inbred line population (PR-15) developed from a cross between ‘CDC 1-2347-144’ and ‘CDC Meadow’. SNPs identified in this study have the potential to aid selection of pea cultivars with improved disease resistance.

Fine Mapping of QTLs for Ascochyta Blight Resistance in Pea Using Heterogeneous Inbred Families

Ascochyta blight (AB) is an important disease of pea which can cause severe grain yield loss under wet conditions. In our previous study, we identified two quantitative trait loci (QTLs) abIII-1 and abI-IV-2 for AB resistance and these QTLs were consistent across locations and/or years in an inter-specific pea population (PR-19) developed from a cross between Alfetta (Pisum sativum) and P651 (P. fulvum). The objectives of this study were to fine map the abIII-1 and abI-IV-2 QTLs using a high density single nucleotide polymorphism (SNP)-based genetic linkage map and analyze identified markers in heterogeneous inbred family (HIF) populations. Selective genotyping of 51 PR-19 recombinant inbred lines was performed using genotyping-by-sequencing (GBS) and the resulting high density genetic linkage map was used to identify eight new SNP markers within the abI-IV-2 QTL, whereas no additional SNPs were identified within the abIII-1 QTL. Two HIF populations HIF-224 (143 lines) and HIF-173 (126 lines) were developed from F6 RILs PR-19-224 and PR-19-173, respectively. The HIF populations evaluated under field conditions in 2015 and 2016 showed a wide range of variation for reaction to AB resistance. Lodging score had significant positive (P < 0.001) correlation with AB scores. HIFs were genotyped using SNP markers within targeted QTLs. The genotypic and phenotypic data of the HIFs were used to identify two new QTLs, abI-IV-2.1 and abI-IV-2.2 for AB resistance within the abI-IV-2 QTL. These QTLs individually explained 5.5 to 14% of the total phenotypic variation. Resistance to lodging was also associated with these two QTLs. Identified SNP markers will be useful in marker assisted selection for development of pea cultivars with improved AB resistance.

Phytoremediation of Heavy Metal-Contaminated Soil Using Bioenergy Crops

Heavy metal contamination of soils affects large areas worldwide. Excessive amount of metals, whether essential or nonessential, adversely affects the health of wildlife, humans, and plants and makes the land unusable for agricultural production. Phytoremediation, a sustainable, environment-friendly, and potentially cost-effective technology, can be used to decontaminate heavy metal-contaminated land. Use of nonfood, dedicated bioenergy crops for remediation of heavy metal-polluted sites has the advantage that biomass produced can be used to generate bioenergy, a cheaper, safer, sustainable, and renewable energy source compared to fossil fuels, avoids direct competition with food, and uses land unsuitable for growing food crops. Identifying dedicated bioenergy crops suitable for a particular metal-contaminated land and strategies to increase their phytoremediation potential are important for the success of this approach. Some dedicated bioenergy crops including poplars (Populus spp.), willows (Salix spp.), elephant grass (Miscanthus × giganteus), castor bean (Ricinus communis), and switchgrass (Panicum virgatum) can tolerate high concentrations of heavy metal, accumulate metal, and grow well on contaminated lands. Phytoremediation potential of these crops can be further improved by the effective use of metal solubilizing agents, endophytic bacteria, and genetic engineering. A better understanding of the mechanisms of heavy metal uptake, translocation, accumulation, and tolerance in normal and metal hyperaccumulator plants will help scientists to develop effective and economic transgenic bioenergy crops for remediation of heavy metals in soil.

Amorphophallus paeoniifolius corm: A potential source of peroxidase for wide applications

ABSTRACT Peroxidases have wide applications in different areas including chemical synthesis, medicine, food industry, bioremediation of wastewater, biosensing, and biotechnology. Amorphophallus paeoniifolius (elephant foot yam) is an attractive source of enzymes; however, no effort has been made to assess peroxidase enzyme from this source. Therefore, the objectives of this study were to evaluate and compare peroxidases from corms of elephant foot yam and roots of Dacus carota (carrot) and Aramoracia rusticana (horseradish). Elephant foot yam corm peroxidase (ECP) demonstrated 4.5 times higher specific activity compared with carrot root peroxidase (CRP). ECP showed retention of high activity over a broad pH range and had higher temperature optima and thermal stability compared with CRP and horseradish peroxidase (HRP). The calculated KM values of ECP, CRP, and HRP for the substrates guaiacol and hydrogen peroxide were 4.5 mM and 307.8 µM, 4.6 mM and 55.5 µM, and 3.5 mM and 413.0 µM, respectively. Peroxidases are used for the bioremediation of wastewater contaminated with hazardous aromatic compounds. Heavy metals such as cadmium (Cd2+), lead (Pb2+), and toxic compounds such as sodium azide (NaN3) are often present in wastewater along with aromatic compounds. Results showed activation of ECP and inhibition of HRP at 250 and 500 µM concentrations of Cd2+ and Pb2+. Treatment with 1 mM NaN3 led to 8.4%, 55.5%, and 11.0% inhibition in the activities of ECP, CRP, and HRP, respectively. Overall, our results suggest that elephant foot yam can be used as a rich and convenient source of peroxidase for various applications including wastewater remediation.