Excision of Ds1 from the genome of maize streak virus in response to different transposase-encoding genes.

We have previously established a reverse genetic system for studying excision of the transposable element Ds1 in maize plants. Ds1 carried by the genome of maize streak virus (MSV) is introduced into maize plants by agroinfection. Excision of Ds1 from the MSV genome depends on the presence of an active Ac element in the recipient maize plants. With the purpose of exploiting MSV-Ds1 as vector for maize transformation, we studied different genes encoding the transposase (TPase) for their efficiency of activating Ds1 excision. These genes were inserted in the same T-DNA carrying MSV-Ds1 and introduced into maize plants by Agrobacterium-mediated transformation. We showed that the wild-type TPase transcribed by the 2' promoter produced much higher efficiency of Ds1 excision than that transcribed by the Ac promoter. In contrast to what had been observed in tobacco and petunia, the truncated TPase (103-807) lacking the amino-terminal 102 amino acids gave a much more reduced Ds1 excision efficiency than the wild-type TPase when both genes were transcribed by the 2' promoter.