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Plant Biotechnology
Published in Firdos Alam Khan, Biotechnology Fundamentals, 2020
Because the sense and the antisense RNAs are complementary to each other, they would pair to produce dsRNA molecules. This event makes the mRNA unavailable for translation. At the same time, the RNA double strand is attacked and degraded by dsRNA-specific RNases. Finally, these events may somehow lead to the methylation of the promoter and coding regions of the normal gene, resulting in the silencing of the endogenous gene. The application of antisense RNA technology is explained using the slow ripening of the tomato as an example. In the tomato, the enzyme polygalacturonase (PG) degrades pectin, which is the major component of the fruit cell wall. This leads to the softening of the fruit and deterioration in fruit quality. Transgenic tomatoes have been produced that contain an antisense construct of the gene encoding PG. These transgenics show a drastically reduced expression of PG and markedly slower ripening and fruit softening. This has greatly improved the shelf life and the general quality of tomato fruits. Such tomatoes are being marketed in the United States under the name “Flavr Savr.”
Selection and Improvement of Industrial Organisms for Biotechnological Applications
Published in Nduka Okafor, Benedict C. Okeke, Modern Industrial Microbiology and Biotechnology, 2017
Nduka Okafor, Benedict C. Okeke
During post-harvest transportation of fruits to supermarkets, these fruits sometimes ripen and become soft due to the natural processes which go on within the fruit. These natural processes include the production of polygalacturonase (PG) (which hydrolyzes pectin) and cellulases by the fruit. In tomatoes, the softening of the fruit is inhibited by engineering an anti-sense PG producing gene into the plant, enabling the fruit to ripen on the plant before harvesting instead of harvesting them while still green. Such tomatoes have a longer shelf life while retaining the taste of regular tomatoes. The genetically engineered tomato known as Flavr Savr was approved by the FDA in 1994 as safe for human use. In anti-sense technology, a gene sequence is inserted in the opposite direction, so during transcription, mRNA complimentary to the normal RNA is produced. The anti-sense mRNA therefore binds to the normal inhibiting translation. The net result is that the gene is shut off, and in the particular case of PG, the fruit-softening enzyme is reduced to about 1% of the normal, thereby inhibiting softening of the fruit and possible microbial attack thereafter.
Glossary of scientific and technical terms in bioengineering and biological engineering
Published in Megh R. Goyal, Scientific and Technical Terms in Bioengineering and Biological Engineering, 2018
Polygalacturonase (PG) is an enzyme which catalyzes the breakdown of pectin. A tomato engineered to contain an antisense-PG gene succeeded in delaying the onset of softening, by inhibiting the expression of PG.
Effect of PCM-based cold storage system under periodic and continuous operations on physico-chemical characteristics of mango (Mangifera indica L.) fruit and performance evaluation of mango cold storage systems
Published in International Journal of Ambient Energy, 2022
K. Karthikeyan, Vairavan Mariappan, P. Sarafoji, K. Uma Bharathi, M. Loganathan, M. Jaya Bharata Reddy, R. Anish
The loss of textural quality in fruits is closely associated with the degradation of cell wall pectins, hemicellulose and cellulose components due to the expression and activity of cell-wall-degrading enzymes (Sun et al. 2013). The pectin substances are the main structural elements in the primary cell wall and regulate cell adhesion. During ripening, the main cell-wall-degrading enzymes, such as polygalacturonase (PG), pectin methylesterase (PME), pectate lyases, 1,4-β-d-glucanase/glucosidase and β-galactosidase (β-gal), dissolved the concentration of cell wall pectin and led solubilisation and depolymerisation of cell wall pectin polysaccharide (Goulao and Oliveira 2008). Cold storage inhibits the activities of cell-wall-degrading enzymes closely related to fruit softening by reducing the rate of metabolic processes during senescence (Deng et al. 2014), resulting in maintaining firmness in the fruit. In this study, mango fruits stored in G24, P12 and P24 storage fruits showed higher firmness retention than fruits stored in G12 and control storage conditions. Fruits stored in P12 and P24 storage conditions indicate results by reducing cell-wall-degrading enzyme activities, polysaccharides solubilisation, and delaying ripening. A significant finding of peel firmness retention by P12 storage condition is concordance with the previous study reported using an evaporative cooler whose temperature was maintained between 14.3°C–19.2°C (Tefera, Seyoum, and Woldetsadik 2007).
Effect of different carbon sources on the growth and enzyme production of a toxigenic and a non-toxigenic strain of Aspergillus flavus
Published in Preparative Biochemistry & Biotechnology, 2021
María Teresa Alvarez-Zúñiga, Diana Castañeda García, Guillermo Aguilar Osorio
Since xylanases and pectinases are considered pathogenic factors,[6] they are of special interest. The number of proteins related to xylan degradation is shown in Fig. 3a. Of a total of 624 CAZymes, 174 were identified as putative xylanases, these proteins were distributed in 30 families, the most abundant family, GH3 family (with 24 proteins), which comprises xylan 1,4-β-xylosidase (EC 3.2.1.37), α-L-arabinofuranosidase (EC 3.2.1.55), exo-xyloglucanase (EC 3.2.1.155) and other enzymes including those that participate in the cellulose degradation. The enzymes of this family are known to exhibit a combination of activities, have possible roles in cellulosic biomass degradation, turnover the cell architecture components of plant and bacteria, recycling, and in pathogen defense.[19,20] Second is the GH43 family (21 proteins) where are mainly found β-xylosidase (EC 3.2.1.37), α-L-arabinofuranosidase (EC 3.2.1.55), xylanase (EC 3.2.1.8), etc. Some enzymes from GH43 have α-L-arabinofuranosidases or β-D-xylosidase activity or both activities (bifunctional), often displaying both activities on aryl-glycoside substrates[21] an important characteristic for xylan degradation. For pectin degradation (Fig. 3b), 57 proteins were found distributed in 10 families, being GH28 family the most abundant, 21 proteins which comprise polygalacturonase (EC 3.2.1.15); α-L-rhamnosidase (EC 3.2.1.40); exo-polygalacturonase (EC 3.2.1.67), exo-polygalacturonosidase (EC 3.2.1.82) among others. Members of this family are important extracellular enzymes for both pathogenic and saprotrophic fungi.[22]Aspergillus flavus also have 16 genes distributed in PL1, PL3, and PL9 families that comprised mainly pectate lyases (EC 4.2.2.2), pectin lyase (EC 4.2.2.10) exo-pectate lyase, and exopolygalacturonate lyase (EC 4.2.2.9). Family PL1 mainly displays activities of pectate lyases and pectin lyases and is one of the largest families of PL class in fungi.[23] Pectinases are important since they modify the structure of the cell wall increasing the accessibility of the rest of the enzymes, are decisive in the infection process and may be related to fungal virulence.[24] This cluster of proteins makes it a good potential candidate not only for the degradation of xylan and pectin or substrates with a high content of these polysaccharides, but also a successful pathogen.