Mohammad Irfan

Physiological changes induced by chromium stress in plants: an overview

This article presents an overview of the mechanism of chromium (Cr) stress in plants. Toxic effects of Cr on plant growth and development depend primarily on its valence state. Cr(VI) is highly toxic and mobile whereas Cr(III) is less toxic. Cr-induced oxidative stress involves induction of lipid peroxidation in plants that cause severe damage to cell membranes which includes degradation of photosynthetic pigments causing deterioration in growth. The potential of plants with the adequacy to accumulate or to stabilize Cr compounds for bioremediation of Cr contamination has gained engrossment in recent years.

Fruit ripening mutants reveal cell metabolism and redox state during ripening.

Ripening which leads to fruit senescence is an inimitable process characterized by vivid changes in color, texture, flavor, and aroma of the fleshy fruits. Our understanding of the mechanisms underlying the regulation of fruit ripening and senescence is far from complete. Molecular and biochemical studies on tomato (Solanum lycopersicum) ripening mutants such as ripening inhibitor (rin), nonripening (nor), and never ripe (Nr) have been useful in our understanding of fruit development and ripening. The MADS-box transcription factor RIN, a global regulator of fruit ripening, is vital for the broad aspects of ripening, in both ethylene-dependent and independent manners. Here, we have carried out microarray analysis to study the expression profiles of tomato genes during ripening of wild type and rin mutant fruits. Analysis of the differentially expressed genes revealed the role of RIN in regulation of several molecular and biochemical events during fruit ripening including fruit specialized metabolism and cellular redox state. The role of reactive oxygen species (ROS) during fruit ripening and senescence was further examined by determining the changes in ROS level during ripening of wild type and mutant fruits and by analyzing expression profiles of the genes involved in maintaining cellular redox state. Taken together, our findings suggest an important role of ROS during fruit ripening and senescence, and therefore, modulation of ROS level during ripening could be useful in achieving desired fruit quality.

Induction of Senescence and Identification of Differentially Expressed Genes in Tomato in Response to Monoterpene

Monoterpenes, which are among the major components of plant essential oils, are known for their ecological roles as well for pharmaceutical properties. Geraniol, an acyclic monoterpene induces cell cycle arrest and apoptosis/senescence in various cancer cells and plants; however, the genes involved in the process and the underlying molecular mechanisms are not well understood. In this study, we demonstrate that treatment of tomato plants with geraniol results in induction of senescence due to a substantial alteration in transcriptome. We have identified several geraniol-responsive protein encoding genes in tomato using suppression subtractive hybridization (SSH) approach. These genes comprise of various components of signal transduction, cellular metabolism, reactive oxygen species (ROS), ethylene signalling, apoptosis and DNA damage response. Upregulation of NADPH oxidase and antioxidant genes, and increase in ROS level after geraniol treatment point towards the involvement of ROS in geraniol-mediated senescence. The delayed onset of seedling death and induced expression of geraniol-responsive genes in geraniol-treated ethylene receptor mutant (Nr) suggest that geraniol-mediated senescence involves both ethylene dependent and independent pathways. Moreover, expression analysis during tomato ripening revealed that geraniol-responsive genes are also associated with the natural organ senescence process.

Impact of sodium nitroprusside on nitrate reductase, proline content, and antioxidant system in tomato under salinity stress

The present study was carried out to elucidate the protective role of sodium nitroprusside (SNP) against salt (NaCl) stress given as seed soaking in tomato (Solanum lycopersicum Mill. cv. K-21). For this experiment prior to sowing, the surface sterilized tomato seeds were soaked in different concentrations of NaCl solution (50, 100, and 150 mM) for 8 hours. Some NaCl soaked seeds were then transferred to the 10−5 M of SNP solution for 8 hours. The plants were sampled at 60 DAS to assess the nitrate reductase activity, proline content and the activities of antioxidant enzymes. The antioxidant enzyme activity and proline content increased in the plants where SNP was applied as a follow up treatment of the NaCl as seed soaking over the control plants thereby providing stress tolerance to the plants. In case of the nitrate reductase activity the toxic effects generated by the lowest concentration of NaCl (50 mM) was completely neutralized by SNP and partly at higher concentrations (100/150 mM). These results suggest that nitric oxide can be used as a stress alleviator in plants which are grown in the soil contaminated with salinity stress.

Fruit Ripening Regulation of α-Mannosidase Expression by the MADS Box Transcription Factor RIPENING INHIBITOR and Ethylene

α-Mannosidase (α-Man), a fruit ripening-specific N-glycan processing enzyme, is involved in ripening-associated fruit softening process. However, the regulation of fruit-ripening specific expression of α-Man is not well understood. We have identified and functionally characterized the promoter of tomato (Solanum lycopersicum) α-Man to provide molecular insights into its transcriptional regulation during fruit ripening. Fruit ripening-specific activation of the α-Man promoter was revealed by analysing promoter driven expression of beta-glucuronidase (GUS) reporter in transgenic tomato. We found that RIPENING INHIBITOR (RIN), a MADS box family transcription factor acts as positive transcriptional regulator of α-Man during fruit ripening. RIN directly bound to the α-Man promoter sequence and promoter activation/α-Man expression was compromised in rin mutant fruit. Deletion analysis revealed that a promoter fragment (567 bp upstream of translational start site) that contained three CArG boxes (binding sites for RIN) was sufficient to drive GUS expression in fruits. In addition, α-Man expression was down-regulated in fruits of Nr mutant which is impaired in ethylene perception and promoter activation/α-Man expression was induced in wild type following treatment with a precursor of ethylene biosynthesis, 1-aminocyclopropane-1-carboxylic acid (ACC). Although, α-Man expression was induced in rin mutant after ACC treatment, the transcript level was less as compared to ACC-treated wild type. Taken together, these results suggest RIN-mediated direct transcriptional regulation of α-Man during fruit ripening and ethylene may acts in RIN-dependent and -independent ways to regulate α-Man expression.

Insights into transcriptional regulation of β-D-N-acetylhexosaminidase, an N-glycan-processing enzyme involved in ripening-associated fruit softening

Highlight text Ripening-specific expression of β-Hex, a gene involved in the fruit-softening process, is transcriptionally regulated by the MADS-box transcription factor RIN in SlASR1-dependent and -independent manners.

Improving nutritional quality and fungal tolerance in soya bean and grass pea by expressing an oxalate decarboxylase

Soya bean (Glycine max) and grass pea (Lathyrus sativus) seeds are important sources of dietary proteins; however, they also contain antinutritional metabolite oxalic acid (OA). Excess dietary intake of OA leads to nephrolithiasis due to the formation of calcium oxalate crystals in kidneys. Besides, OA is also a known precursor of β-N-oxalyl-L-α,β-diaminopropionic acid (β-ODAP), a neurotoxin found in grass pea. Here, we report the reduction in OA level in soya bean (up to 73%) and grass pea (up to 75%) seeds by constitutive and/or seed-specific expression of an oxalate-degrading enzyme, oxalate decarboxylase (FvOXDC) of Flammulina velutipes. In addition, β-ODAP level of grass pea seeds was also reduced up to 73%. Reduced OA content was interrelated with the associated increase in seeds micronutrients such as calcium, iron and zinc. Moreover, constitutive expression of FvOXDC led to improved tolerance to the fungal pathogen Sclerotinia sclerotiorum that requires OA during host colonization. Importantly, FvOXDC-expressing soya bean and grass pea plants were similar to the wild type with respect to the morphology and photosynthetic rates, and seed protein pool remained unaltered as revealed by the comparative proteomic analysis. Taken together, these results demonstrated improved seed quality and tolerance to the fungal pathogen in two important legume crops, by the expression of an oxalate-degrading enzyme.

Brassinosteroids: under biotic stress

Brassinosteroids are the steroidal plant hormones, key regulators of growth and metabolism in metabolically active tissues. Their interplay ensures either the accelerated growth or differentiation in meristematic tissues or induces the defense responses in biotically challenged tissues, stopping the growth responses in concentration dependent manner. A rationale of highly active growth regulators and classical phytohormones, based on external cues and endogenous developmental program, ascertains the fate of localized tissue for the sake of whole plant, may induce hypersensitive response based PCD, activating LAR and/or SAR. A shift of growth metabolism towards defense strategies is evidenced in several Arabidopsis and other BR mutants suggesting their antagonistic role. However, specific interaction of BRs with well known other phytohormones in suppressing the growth responses under biotic stress, have been tried to underline in the present survey.

A comprehensive analysis of Candida albicans phosphoproteome reveals dynamic changes in phosphoprotein abundance during hyphal morphogenesis

The morphological plasticity of Candida albicans is a virulence determinant as the hyphal form has significant roles in the infection process. Recently, phosphoregulation of proteins through phosphorylation and dephosphorylation events has gained importance in studying the regulation of pathogenicity at the molecular level. To understand the importance of phosphorylation in hyphal morphogenesis, global analysis of the phosphoproteome was performed after hyphal induction with elevated temperature, serum, and N-acetyl-glucosamine (GlcNAc) treatments. The study identified 60, 20, and 53 phosphoproteins unique to elevated temperature-, serum-, and GlcNAc-treated conditions, respectively. Distribution of unique phosphorylation sites sorted by the modified amino acids revealed that predominant phosphorylation occurs in serine, followed by threonine and tyrosine residues in all the datasets. However, the frequency distribution of phosphorylation sites in the proteins varied with treatment conditions. Further, interaction network-based functional annotation of protein kinases of C. albicans as well as identified phosphoproteins was performed, which demonstrated the interaction of kinases with phosphoproteins during filamentous growth. Altogether, the present findings will serve as a base for further functional studies in the aspects of protein kinase-target protein interaction in effectuating phosphorylation of target proteins, and delineating the downstream signaling networks linked to virulence characteristics of C. albicans.

Comparison of the Influence of 28-Homobrassinolide and 24-Epibrassinolide on Nitrate Reductase Activity, Proline Content, and Antioxidative Enzymes of Tomato

Brassinosteroids (BRs) are a class of polyhydroxysteroid plant hormones. The sensitivity of a crop to abiotic/biotic stress is a functional aspect of its response as regulated by the efficient internal buildup of hormones like BRs. A better understanding of how the brassinosteroid isomers differentially affect plant responses in tomato (Solanum lycopersicum L.) is necessary to improve production. Plants of cv. K-21 were grown in a net house and foliage was treated with brassinosteroid isomers 28-homobrassinolide (HBL) and 24-epibrassinolide (EBL) at concentrations of 10−6, 10−8, or 10−10 M. Plants responded more to EBL than to HBL. All treatments increased nitrate reductase activity and the antioxidant system with respect to the control. However, the 10−8 M concentration of EBL produced higher nitrate reductase activity and better stimulated the antioxidant system in tomato. In physiological experiments, different concentrations/modes of stress/hormone(s) were tested and justified in biosynthetic or signaling mutants to fix the resistant response in transgenically tailored crops. Physiological studies are an integral part of systematic studies of crop improvement and can provide the basis for molecular experiments.