51. Identify the INCORRECT statements with respect to plastid transformation.
P. Antibiotic used for selection of trasplastomic plant is spectinomycin
Q. Chances of gene escape from transplastomic plants are high
R. Microprojectile bombardment is the method of DNA delivery
S. Levels of transgene expression are low
(A) P, R
(B) 𝑃,𝑄
(C) Q, S
(D) R, S

Plastid transformation, or chloroplast engineering, revolutionizes plant biotechnology by enabling high transgene expression with maternal inheritance. This SEO-optimized guide breaks down a key multiple-choice question (MCQ) on its core aspects, identifies the correct answer (C) Q and S, and explains each option for students and researchers in genetics and plant sciences.

Correct Answer

The correct choice is (C) Q, S. Statements Q (“Chances of gene escape from transplastomic plants are high”) and S (“Levels of transgene expression are low”) are incorrect. Plastid transformation features low gene escape due to maternal inheritance and exceptionally high transgene expression from multicopy plastid genomes.​

Statement P: Spectinomycin Selection

Spectinomycin serves as the standard antibiotic for selecting transplastomic plants. The aadA gene confers resistance by detoxifying spectinomycin, which otherwise inhibits plastid 70S ribosomes, allowing green resistant sectors to regenerate on selective media. This statement is correct, as confirmed in tobacco, Arabidopsis, and other models.​

Statement Q: Gene Escape Risk

Chances of gene escape are not high but extremely low in transplastomic plants. Plastid genomes transmit maternally via pollen in most crops, preventing transgene spread through paternal routes and enhancing containment over nuclear transformation. This makes Q incorrect, a key advantage for biotech safety.​

Statement R: DNA Delivery Method

Microprojectile bombardment (biolistics) is the primary method for plastid DNA delivery. Gold or tungsten particles coated with transformation vectors penetrate cell walls to target plastid genomes, enabling stable integration via homologous recombination. R is correct, though PEG-mediated alternatives exist for protoplasts.​

Statement S: Transgene Expression

Transgene expression levels are high, not low, in plastids—often 10-100x nuclear levels due to thousands of genome copies per cell and no gene silencing. This suits industrial proteins like vaccines or enzymes, contradicting S. Thus, S is incorrect.​