Give information about pest resistant plants. Explain $\rm {RNA}$ interference.

$\rightarrow$ Several nematodes parasitise a wide variety of plants and animals including human beings.

- A nematode meloidegyne incognitia infects the roots of tobacco plants and causes a great reduction in yield. A novel strategy was adopted to prevent this infestation which was based on the process of $RNA$ interference.

- $RNAi$ takes place in all eukaryotic organisms as a method of cellular defense.

This method involves silencing of a specific $mRNA$ due to a complementary dsRNA molecule that binds to and prevents translation of the $mRNA.$

The source of this complementary $RNA$ could be from air infection by viruses having $RNA$ genomes or mobile genetic elements (transposons) that replicate via an $RNA$ intermediate.

- Using Agrobacterium vectors, nematode specific genes were introduced into the host plant.

The introduction of $DNA$ was such that it produced both sense and antisense $RNA$ in the host cells.

These two $RNA's$ being complimentary to each other formed a double stranded ($dsRNA$) that initiated $RNAi$ and thus silenced the specific $mRNA$ of the nematode.

The consequence was that the parasite could not servive in a transgenic host expressing specific interfering $RNA$. The transgenic plant therefore got itself protected from the parasite.