Gene silencing role in reducing HCN contents of Sorghum

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What will happen if we reduce the cyanide contents of sorghum?? Surely it will be an advancement in our agricultural technology. Sorghum (Sorghum bicolor) is a grain as well as a forage crop. As grain crops, it is used for human consumption and as a forage crop, its vegetative part is mainly used for animal feed so it’s a dual-purpose crop. Main issue for using sorghum as forage as well as for human consumption is its cyanide contents. Cyanide is a chemical compound which is present in plants by chemical bonding with glucose. On hydrolyzes, glucose molecule is released and cyanide reacts with hydrogen to form hydrogen cyanide.As cyanide is toxic for animals it protects them against herbivores and acts as a signaling molecule too. But its toxic effects are more than its benefits.It damages nervous system of animals may kill them even is minutes. It also affects respiratory system of mammals making oxygen absorption difficult. Technically cyanide contents of sorghum start increasing at an early age after germination. Mainly cyanide contents of plants depend upon its chronological age i.e. old leaves have high cyanide contents and young leaves are low in cyanide contents.  A small family of genes i.e. 5 which codes for two main enzymes which play an important role in cyanide production.These genes are CYP79A1 and CYP71E1. More expression of these genes more will be a number of enzymes produced by these enzymes.Hence more will be the production of cyanide in tissues. It also depends upon nitrogen fertilizers i.e. more the use of nitrogen fertilizers more will be the production of cyanide in plants. Although a significant amount of HCN is detoxified by enzymes like B-cyanoalanine synthase sometimes even low contents of cyanide are enough to kill a person. So, we need a mechanism that stops the production of cyanide. Out of 5 genes coding for HCN production CYP79A1 plays a major role in cyanide production.The regulation of this gene can be silenced through the gene methylation i.e. transfer of a methyl group to 5 carbon of cytosine or adenine but mostly cytosine is methylated that inhibits its transcription. So, there will be a low level of mRNA which means a low level of cyanide in these plants. Methylation of a gene is done using enzymes. As animal kingdom plants also possess some unique enzymes which are important for methylation i.e. DRM2, MET1, and CMT3. CMT3 is a unique enzyme of plants completely different from animals. There are two steps in DNA methylation. In the first step, a methyl group is transferred t to CYP79A1 gene strand. In second step enzyme will add methyl group to daughter strand for its maintenance. After methylation of gene confirmation will be done. There are two types of enzymes. One type cut DNA at non-methylated sites while other type cuts at non-methylated site. Through their RFLP patterns genotype containing methylated gene can be identified. Confirmation can be done in lab by raising seedling then testing them for field. Those genotypes which produce a negligible amount of cyanide infield can be introduced as new biotechnological variety.


Published in: Volume 08 Issue 38

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