Construção de cassetes de expressão para silenciamento gênico de fatores antinutricionais da soja, via interferência por RNA / Construction of expression cassettes for RNAi-based silencing of genes encoding antinutritional factors in soybean seeds

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

Soybean is one of the most important crops in the world extensively used as a food and feed source. However, the proteins present in soybean seeds are not considered ideal because they contain low amounts of the essential amino acids methionine and lysine. Adverse nutritional and other effects following consumption of raw soybean meal have been attributed to the presence of endogenous inhibitors of digestive enzymes and allergenic factors. Among these proteins are the P34 protein and the Bowman-Birk protease inhibitors. The absence of these factors would increase the nutritional quality of the soybean seeds, as well as the availability of this product to large number of consumers. Recent advances in plant biotechnology have enabled the silencing of specific genes. One of the techniques used to achieve this goal is RNA interference (RNAi). This method of posttranscriptional gene silencing is highly efficient, especially when the construct results in the formation of a intron-spliced hairpin RNA. It is proposed that RNAi works by enzymatic RNA degradation induced by double-stranded RNA. The main goal of this work was to construct expression cassettes for RNAi-based silencing of genes encoding antinutritional factors in soybean seeds. To achieve seed-specific expression, specific primers were designed for the amplification of the promoter region of the alpha-subunit of the beta-conglycinin gene. Appropriate restriction sites - Sac I and Xho I - were added to the primers which were used to amplify a 634 bp fragment. This product was cloned into a pGEMTEasy vector and cloning was verified by PCR, enzymatic digestion and sequencing. The sequenced clone was analyzed in silico for identification of cis-elements related to seed specific expression. The elements TATA box, CAAT box, RY LEG box and RY FLEB box were found. The fragment of interest was isolated from vector pGEM-TEasy by cleavage with enzymes Sac I and Xho I and inserted in the expression vector pKANNIBAL. This new vector was designated pBKN. For the construction of the expression cassettes, primers were designed according to published sequences deposited in the GenBank. The fragments of interest were isolated by the RT-PCR method using RNA isolated from soybean seeds. RT-PCR was also used to analyze the expression of the gene of interest in the seed and in other organs of the plant (root, stem and leaves). These analyses showed that the expression of these genes was continuous and abundant during all stages of seed development, and the corresponding transcripts were present in all organs analyzed. The fragments obtained by RT-PCR were sequenced and their identity was confirmed by BLAST analysis. To clone the sense sequence, the vectors pKANNIBAL and pBKN, and the fragments of interest were cleaved with enzymes Xho I and Kpn I. The ligation reaction was catalyzed by T4 DNA ligase and competent cells of Escherichia coli were transformed by heat shock. Cloning was verified by PCR and enzymatic digestion. The cloning of the antisense fragment was done using restriction enzymes Xba I and Cla I and vectors containing the sense fragments. The complete expression cassettes were cloned into the binary vector pCAMBIA 3301 and verified by PCR.

ASSUNTO(S)

soybean rnai genetica molecular e de microorganismos antinutritional factors soja fatores antinutricionais rnai

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