The Use of Antisense Procedures in the Genetic Engineering of Plants for Crop Improvement

Crop improvement is the main strategy for a farmer. After rediscovery of Mendels laws of Heredity at the very beginning of the last century, this got a scientific base. Since then several new principles and technologies for proven and promising and potential applications have come into practice. Initially plant breeding between two desirable parents by proper selections in the subsequent generations was the main strategy. During the last thirty years deeper molecular biology insights have opened new opportunities. New technologies for foreign DNA movement into a host crop plant have been developed. This was achieved by introducing a DNA sequence extracted, developed or designed for a desired trait into a cell of the host crop plant cell and regeneration of a whole plant thereof. Such a technology though welcome had its limitations that this also many undesired characters in the host. Advances in a closer and broader understanding of the whole nucleic acids has made possible a method which facilitates desirable alterations within a crop plant genome itself.   

Antisense Technology  Conceptually this implies shutting (silencing) a gene from producing the corresponding protein for its effects such as function, shape andor color of  an organ. In other words, a molecule that interacts with the complementary strands of nucleic acids is called the antisense molecule. For example in 1994, the polygalacturonase gene (responsible for fruit ripening) in tomato was suppressed to delay the ripening dependent softening of the fruit, thus prolonging a the shelf life
The Antisense Concept - Antisense RNA concept is reverse of the normal process in which the messenger RNA (complementary mRNA) is transcribed from DNA. From this mRNA, in a normal situation an amino acid sequence or a peptide is translated finally to form a protein. On the other hand in the ANTISENSE technology, the translated product, mRNA, is not allowed to proceed further in the step of translation. This mRNA is made to produce its own complementary strand and thus form a double stranded nucleic acid. This is thus disabled from recognition by the cellular protein synthesis machinery. Many times the double stranded nucleic acid sequence is not stable and gets disintegrates soon after formation.

Creating Resistances to Viral Diseases - Resistance to Barley Yellow Vein Mosaic Virus (BYMV, a Poty virus group  a viral threat to many leguminous and solanaceous crop species and other family crops) was created by creating an Antisense RNA from C-terminal part of its coat protein gene. This was attached to the 3- prime side of the total non-coding region of the BYMV. This was then attached to the Cauliflower Mosaic Virus 35 S promoter sequence (CAMV 35 S). The CAMV 35 S promoter activates the functioning of the genetic sequence under its control. The total structure was then introduced  into Nicotiana benthamiana. The thus engineered tobacco plants were allowed to proceed through normal sexual cycles for seed production. The resultant progeny when challenged with the BYM Virus showed mild resistant reaction unseen on the non-engineered progeny.
The Success -    After several experimentally validated proofs of feasibility and success of this concept, this has been successfully employed in many other area of crop improvement. They include over-production of flower color in ornamentals, viral resistances in many other crops such as papaya by the ring spot coat protein has been possible.
A closely resembling technology is that of the RNA interference (RNAi) technology has been developed and potential uses have been found in for increased tolerances to biotic and abiotic stresses in crop plants. In humans this idea is being applied in the context of diseases.


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