Key enzymes characterization to the control of lysine metabolism in genetic modified corn (Zea mays L.)

Author(s)

Vanessa Rizzi

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2013-05-24

Examining board members

Ricardo Antunes de Azevedo; Rogério Falleiros Carvalho

• Advisor: Ricardo Antunes de Azevedo

Abstract

Lysine is an essential amino acid and one of the limiting factors for the use in cereals such as corn feed therefore, without supplementation; it does not allow obtaining a balanced diet. In order to improve the nutritional quality of cereals, several attempts have been made based on the results about routes of metabolism of lysine in plants and accumulation of storage proteins in endosperm. Ambrozevicius (2010) with the objective of producing transgenic corn plants with high content of lysine used a strategy of expression of storage proteins from other plant species which are rich in lysine, it means, through the expression of a heterologous protein: zeolin. This work aimed to study the 6 events processed expressing zeolina in F3 generation, featuring the storage proteins, the profile of amino acids and enzymes involved in the metabolism of lysine in genetically modified corn, in order to understand the possible biochemical changes which may have been generated by the transformation, and that may have led to the increase of essential amino acids in transgenic material The storage protein profile of transformed events exhibited reduction in the proportion of zein II and glutelins compared to control HiII, and yet very discrete increments of globulin, but not for all events processed. In the composition of soluble amino acids, it was observed increments in concentration of amino acids forming part of the metabolic pathway of aspartic acid: Lysine, methionine, threonine and isoleucine. For the amino acids incorporated into proteins, it was observed increments in the levels of lysine in the transformed events of globulin and glutelin fraction, both in relation to the control HiII. On the other hand, zein fraction I had the highest total amino acid content in all transformed events. The analysis of the enzymes involved in the metabolism of lysine revealed that changes occurred in two enzymes, the first enzyme involved in the synthesis of lysine, aspartate kinase (AK) and the second involved in the degradation of lysine, lysine ketoglutarate reductase (LOR). Although other enzymes involved in the synthesis and degradation of lysine have also been changed, the results were variable for different events. This work showed that the expression of heterologous protein zeolina caused changes in the composition of protein fractions, in the content of soluble amino acids and amino acids incorporated in consequence of changes in enzymes involved in the synthesis and degradation of lysine. The results suggest that the expression of heterologous protein zeolina, which has the need for incorporation of lysine in its structure, may have changed the aspartic acid pathway to meet the new demand for lysine. These changes may include the increase in AK enzyme activity, which is the first enzyme of the pathway leading to the synthesis of this amino acid and also a reduction in the activity of the enzyme degradation LOR, since the excess free lysine would be degraded is incorporated into the new protein. (AU)

• FAPESP's process: 11/03134-2 - Characterization of key enzymes of lysine control metabolism in maize (Zea mays L.) genetically modified
• Grantee: Vanessa Rizzi
• Support Opportunities: Scholarships in Brazil - Master