Why are the carotenoid levels in GR1 and GR2 higher in this Golden Rice than in the version published by Potrykus and Beyer?
There are several likely reasons. In both strains the gene constructs used by Syngenta were slightly different from the original construct. Whilst the two carotenoid biosynthesis genes are functionally the same, the control element of one of the genes was exchanged. In the new strains the phytoene desaturase gene crtI is expressed using a seed-specific promoter rather than a constitutive promoter (i.e. active throughout the plant). This may have beneficially affected the amount of carotenoid that is accumulated in the grain. In GR2 the Narcissus phytoene synthase gene psy used in the original construct was exchanged for a maize homolog. Also, in their work Syngenta was able to generate hundreds of individual Golden Rice transformants and within they found more plants with particularly high levels of carotenoid accumulation. The experiments of Potrykus and Beyer produced far fewer plants and the chances of finding plants with high levels were therefore lower. It is normal to expect a ra
There are several likely reasons. In both strains the gene constructs used by Syngenta were slightly different from the original construct. Whilst the two carotenoid biosynthesis genes are functionally the same, the genetic control element of one of the genes was exchanged. In the new strains the phytoene desaturase gene crtI is expressed using a seed-specific promoter rather than a constitutive promoter (i.e. active throughout the plant). This may have beneficially affected the amount of carotenoid that is accumulated in the grain. In GR2 the Narcissus phytoene synthase gene psy used in the original construct was exchanged for a maize homolog. Also, in their work Syngenta was able to generate hundreds of individual Golden Rice transformants among which the probability of finding plants with particularly high levels of carotenoid accumulation was higher. Potrykus and Beyer produced far fewer plants, as theirs was the proof-of-concept phase of the project. In addition, the rice variety
