Applications of Molecular Biology in Agriculture

Abstract

Detailed knowledge of the processes involved in the central dogma of molecular biology has enabled the direct or indirect use of DNA in molecular characterization, in direct changes of genetic information (named genetic edition), and in the breeding of genetically modified organisms. The three activities have had a major impact on both research and production in agriculture. The characterization seeks to determine the identity of the individuals in the most reliable possible manner to make subsequent genetic diversity analyses, or to register or patent cultivars, or to make diagnoses of the presence of a certain pathogen or insect pest. These activities are usually done based on morphological traits, but these have the disadvantage of a high environmental influence and/or certain subjectivity in the determination. Molecular markers, especially DNA markers, and some isoenzymes overcome this disadvantage. Due to the high resolution they can have, DNA markers are becoming increasingly popular. The vast majority of them are based on the polymerase chain reaction (PCR), with their informative quality being dependent on whether they are co-dominant or dominant. When it is possible to relate an agronomically desirable characteristic with a band of some molecular marker, it is feasible to carry out molecular marker-assisted selection, which potentially has high efficiency. Genetically modified organisms are individuals in which DNA have been modified, either by insertion or deletion of some nucleotides (genetic editing) or by insertion of genes in an unnatural way since it is not through sexual reproduction. Therefore, it is possible to obtain individuals with genes from unrelated species to these via what is known as the recombinant DNA technique. Bioethics and biosafety are concepts usually related to obtaining and using genetically modified organisms.

Knowledge Integration Questions

• 1. Based on the following zymogram:

  

  • (a) Indicate, if any, where polymorphism is detected.

    Considering the position of the bands from the top to the bottom, band 1 is polymorphic (present in varieties 1, 2, 3, and 5 but absent in variety 4), band 2 is also polymorphic (present in variety 4 and absent in 1, 2, 3, and 5), band 3 is also polymorphic (present in 1, 3, 4, and 5 but absent in 2), band 4 is monomorphic (present in all varieties), and band 5 is polymorphic (present in varieties 2, 3, and 5 but absent in 1 and 4).

  • (b) Mention at least four ways in which this zymogram could have been obtained. Of the ones you mentioned, tell which one is more reliable and why.

    The zymogram may be representing total proteins, soluble proteins in some determined fraction, isoenzymes, or DNA. If the bands represent DNA, they can be obtained, for example, using RAPD, RFLP, or AFLP. It could also be microsatellites, but in this case, it would correspond to varieties of a polyploid species since if it were diploid, there would be no more than two bands per variety. DNA markers are more reliable due to the absolute insensitivity to environmental conditions and the stage of development in which the samples are taken.

  • (c) If, when performing an evaluation of 1000 plants of each of the five varieties in relation to their resistance to a virus, it was determined that variety 4 is resistant; and at the same time, we obtain the respective zymograms, which always turned out to be the same as the one presented here, could you take advantage of this situation in plant breeding? Explain.

    Yes, this situation could be used in plant breeding since it could be used to lay the groundwork for a molecular marker-assisted selection program. The fact that all resistant plants exhibit a band, which is absent in susceptible plants (band 2), it gives the opportunity to know whether any other plant (of the same species) will be resistant or not; this can be defined at the seed level. If for future sowings of this species, the presence of the band at the seed level will be determined, only those seeds that have the band should be sown, and discard seeds that do not have the band, thus ensuring the planting of resistant material.

• 2. Suppose you are hired by a company that will be in the business of obtaining transgenic maize, with higher lysine content in its grain. Make an outline of the report that you would present about the idea and the methodology to be used.

  The justification for GM maize production should be considered only if within the species, there are no sources of variability for the trait to be improved (in lysine content in the grain) that would make it possible to obtain a new cultivar by the conventional route. If this is the case, the most expeditious methodology to be used would be the biolistic since the Agrobacterium system has worked very efficiently in dicotyledons but not in monocotyledons such as maize; there are still some problems with the process efficiency. It is necessary to consider the country’s biosafety standards where the new genetically modified cultivar will be released, especially related to the distances that should exist between transgenic and non-transgenic crops to prevent crossing between them; or to the presence of wild species closely related to the crop, which could eventually be pollinated by transgenic plants.