TDNA

TDNA, or T-DNA, stands for transfer DNA. It is a defined segment of DNA originally part of the Ti plasmid (tumor-inducing plasmid) of the soil bacterium Agrobacterium tumefaciens. During natural infection, T-DNA is transferred from the bacterium into plant cells and integrated into the plant genome, where it can alter growth and metabolism.

In its native context, T-DNA is bounded by left and right border sequences that delimit the portion eligible for transfer. The genes within the T-DNA of a tumor-inducing strain encode enzymes for hormone synthesis and opine production, which promote tumor formation and provide a nutrient source for the bacteria.

In genetic engineering, these biological properties are harnessed. The tumor-related genes are removed and replaced by a gene of interest and selectable markers, still flanked by T-DNA borders. The resulting T-DNA region can be transferred into plant cells via Agrobacterium and stably integrated into the plant genome, enabling durable expression.

Mechanism: Vir genes in Agrobacterium process and transport T-DNA, generating a single-stranded T-DNA and delivering it through a type IV secretion system. Once inside the plant nucleus, the T-DNA integrates at random genomic locations, often in transcriptionally active regions, leading to stable transgene expression.

Applications and considerations: T-DNA vectors are widely used for plant genetic engineering, functional genomics, and crop improvement. Limitations include variable integration patterns, potential gene silencing, and host range constraints. Regulatory, environmental, and biosafety considerations govern the use of T-DNA–based methods.