Abla Ebrahim Ali Elawady

Molecular and physiological characterizationof Nicotiana tabacum ferrochelatase

 


Abstract


Ferrochelatase ((FC) protoheme ferro-lyase (EC 4.99.1.1 )) catalyzes the insertion of ferrous ion into protoporphyrin IX (Proto) to form protoheme. FC is a single sub unit enzyme encoded by two genes FCI and FCII. The full-length cDNA sequence encoding tobacco FCII was identified and isolated to produce transgenic plants silencing the FCI gene. Transgenic tobacco plants were generated to analyze the consequences of inactivation of FCI on the expression and the activity in the tetrapyrrole biosynthesis pathway. FCI antisense transformants contained lower FCI transcript levels and a reduced FC activity leading to increased Proto and decreased heme contents. Interestingly, the ALA synthesizing capacity was altered in transgenic lines with FCI inactivation, which can be explained by feedback regulation of heme on the initial step of tetrapyrrole biosynthesis. FCI antisense plants with decreased accumulation of heme, show increased expression of photosynthesis-associated nuclear genes (PhANGs). These data suggest heme as a retrograde signal that modulates PhANG expression in the nucleus in response to tetrapyrrole biosynthesis in chloroplasts. Another central question regards the unambiguous organellar localization of FCI in higher plants. Two FCI-fusion gene constructs with two alternative ATG-initiation codons were designed to demonstrate subcellular localization of FCI. The in situ expression assays revealed sole targeting of FCI into chloroplasts, but not into mitochondria.

Keywords: Ferrochelatase I (FCI). Tetrapyrroles. Nicotiana tabacum. Heme. Chloroplast. Feedback regulation. Retrograde signal.



 Mohamed Hazman

Adaptation to salt stress in rice-How jasmonates contribute to the response to high salinity

 

Botany Institute I, Karlsruhe Institute for Technology (KIT), Germany

Abstract

Salinity is the major environmental factor limiting plant growth and productivity. Due to its sessile lifestyle, plants must adjust their growth and development under such conditions through the integration of hormone signaling at different level of stress. The oxylipin jasmonic acid and its metabolites, collectively known as jasmonates are important plant signalling molecules that mediate responses to biotic and abiotic stresses; nevertheless, its role under salt stress is not completely uncovered. The response of two jasmonate biosynthesis rice mutants (cpm2 and hebiba) to salt stress was investigated in comparison to their wild type.

These genotypes were compared on the level of morphology, physiology and molecular biology. Surprisingly, the phenotype of jasmonate biosynthesis mutants suggested that they are less sensitive to salinity, illustrated by less stress damage symptoms in second and third leaves, and longer roots under salt stress in seedlings exposed to high salt concentrations. Interestingly, both cpm2 and hebiba plants accumulated smaller amounts of Na+ ions in their leaves. Oxidative damage parameters (MDA and H2O2) were higher in wild type leaves. Nevertheless, soluble proline, discussed as an antioxidant and osmoprotectant, was less abundant in the mutants. Furthermore, it was observed that the crude extract of the mutants detoxified in vitro produced reactive oxygen species (ROS) more efficiently than wild type extracts reflecting a higher antioxidative power. The profile of antioxidant enzyme activities showed that Superoxide dismutase (SOD) and Peroxidases (POD), Glutathione Reductase (GR) and Glutathion-s-transferase (GST) performed better in the shoots of both mutants compared to the wild type. Gene expression analysis of selected genes in the signaling pathway of salinity revealed that the mutants showed significantly lower inducibility of the vacuolar Na+/H+ antiporter encoding gene (OsNHX1) suggesting less turgid vacuoles. The role of abscisic acid (ABA) was investigated through measuring the expression of one of the ABA key biosynthesis enzymes OsNCED5 (9-cis-epoxycarotenoid dioxygenase) which was found to be higher in the mutants comparing to WT, nevertheless, the endogenous level of ABA was comparable in both wild type and jasmonate biosynthesis mutants, indicating that not the biosynthesis but the sensitivity in the mutants might be altered. Furthermore it was found that OsNR gene expression (encoding for nitrate reductase, a key enzymes in NO production) was induced by salinity more strongly in the mutants, and the stomatal guard cells of the mutants accumulate more NO than that of the wild type. The endogenous levels of JA, JA-Ile and especially OPDA were elevated in response to salt stress in case of wild type only but not changed in the mutants. Based on these results, we suggest that jasmonates may affect the biosynthesis of NO and in this way alters stomata closure. Due to altered stomatal opening, the transpiration stream might be slower in the mutants leading to less root-to-shoot sodium ions transfer, As a result of transferring less sodium from roots to its leaves, JA biosynthesis mutants suffer less from oxidative stress as its ability to scavenge ROS was not totally damaged by Na+ ions.

Key words:ALLENE OXIDE CYCLASE (AOC), jasmonate, Oryza sativa, oxidative stress, 12-oxophytodienoic acid (12-OPDA), reactive oxygen species (ROS), salinity.


Ali S. Abdelaal, Amr M. Ageez, Abd El-Hadi A. Abd El-Hadi, Naglaa A. Abdallah

Thesis for the degree of

Ph.D. Title: Isolation and Characterization of Gene(s) Responsible for Tolerating Biofuel Production,

Cairo University, Faculty of Agricultur )Genetic ) 

Abstract

Strain tolerance to toxic metabolites remains an important issue in the production of biofuels. Here we examined the impact of overexpressing the heterologous groESL chaperone from Clostridium acetobutylicum to enhance the tolerance of Escherichia coli against several stressors. Strain tolerance was identified using strain maximum specific growth rate () and strain growth after a period of solvent exposure. In comparison with control strain, the groESL overexpressing strain yielded a 27 % increase in growth under 0.8 % (v/v) butanol, a 9 % increase under 1 % (v/v) butanol, and a 64 % increase under 1.75 (g/l) acetate. Moreover, after 10 h, groESL overexpression resulted in increase in relative tolerance of 58 % compared with control strain under 0.8 % (v/v) butanol, 56 % increase under 1 % (v/v) butanol, 42 % increase under 1 % (v/v) isobutanol, 36 % increase under 4 % (v/v) ethanol, 58 % increase under 1.75 (g/l) acetate. These data demonstrate that overexpression of the groESL from C. acetobutylicum in E. coli increased tolerance to several stressors. Solvent tolerant strain of E. coli was developed to be used as a basic strain for biofuel production.


Our Partners

Download Free Premium Joomla Templates • FREE High-quality Joomla! Designs BIGtheme.net