Male sterility in transgenic tobacco plants induced by tapetum-specific deacetylation of the externally applied non-toxic compound N-acetyl-L-phosphinothricin.

A system for the inducible destruction of plant tissues based on the deacetylation of the non-toxic compound N-acetyl-L-phosphinothricin (N-ac-Pt) has been developed. The argE gene product of Escherichia coli, representing a N-acetyl-L-ornithine deacetylase was identified to remove the acetyl-group from N-ac-Pt giving the cytotoxic compound L-phosphinothricin (Pt, glufosinate). Transgenic Nicotiana tabacum plants constitutively expressing the argE gene were constructed. No effect of the bacterial N-acetyl-L-ornithine deacetylase on plant growth and reproduction could be traced. However, application of N-ac-Pt on leaves of the transgenic plants led to the formation of necrotic areas due to the release of Pt. Additionally, due to the uptake of the N-ac-Pt by roots, transgenic shoots grown on medium containing N-ac-Pt bleached within 6-7 days and finally died. Untransformed controls showed no reaction to high amounts of N-ac-Pt applied, either under sterile or under unsterile conditions. In order to construct inducible male-sterile plants, the argE coding region was fused to a DNA fragment carrying sequences homologous to the tobacco TA29 promoter, known to function exclusively in the tapetum. Owing to the tapetum-specific expression of the chimeric gene the application of N-ac-Pt led to empty anthers resulting in male-sterile plants. The sanity of the female reproductive part of the male-sterile flowers could be demonstrated by cross-pollination. Without N-ac-Pt treatment the plants turned out to be completely fertile making fertility restoration in the F1 generation superfluous. The system presented is easy to handle and might be applicable to a wide range of crop plants.