Which enzyme is used in DNA amplification during cDNA cloning?

In the context of cDNA cloning, the correct enzyme used in the amplification of DNA is reverse transcriptase. This enzyme is critical because it synthesizes complementary DNA (cDNA) from an RNA template. In the process of cDNA cloning, reverse transcriptase catalyzes the reverse transcription of messenger RNA (mRNA), converting it into cDNA.

Once the cDNA is synthesized, it can be amplified using DNA polymerase in subsequent steps, such as in PCR (polymerase chain reaction). However, when specifically considering the amplification during the initial step where RNA is turned into cDNA, reverse transcriptase is the key enzyme.

DNA ligase, another enzyme mentioned, is involved in sealing nicks in the phosphate backbone of DNA, but it does not play a direct role in amplification. The term 'agarose ligase' is not a recognized enzyme in this context, and thus it does not pertain to the cDNA amplification process. Therefore, reverse transcriptase is accurately highlighted as the essential enzyme for cDNA synthesis in the context of cloning and amplification of RNA-based sequences.