Question

Early genetic manipulation of petunias included an attempt to engineer dark purple petals. To this end, extra copies of the gene that causes purple pigment was engineered to be produced in the petunia. However, to the surprise of many, the plants carrying the extra copies of the purple gene were completely white or only had patches of color. Molecular analysis revealed that the purple gene was reduced 50-fold in the engineered plants compared to wild type. Provide a possible explanation how this occurred. Also, provide a possible experiment that may overcome this setback

Answer 1

The altered pigmentation in transgenic petunia plants is caused by the RNA interference (RNAi) mechanism

Step-by-step explanation:

The RNA interference mechanism is a naturally occurring mechanism by which single-stranded RNA molecules can bind to complementary mRNAs in order to inhibit gene expression, blocking translation and leading to mRNA degradation. The example above described is a classical genetic experiment (Napoli et al. 1990 ) that showed the existence of the RNAi pathway by the overexpression of a chimeric chalcone synthase (CHS) gene in pigmented petunia flowers, which blocked anthocyanin biosynthesis. In this experiment, irregularly bicolored/white flowers in transgenic petunias containing exogenous pigmentation genes were developed. The co‑suppression of gene expression was produced by the high-copy-number transcription of the CHS transgene, showing the existence of an undescribed RNAi silencing mechanism. Somatic reversion of the altered phenotype can be achieved by restoring the normal mRNA levels for these pigmentation genes, e.g., by a progeny testing in order to eliminate transgenic CHS expression.