MALE-STERILITY IN TRANSGENIC TOBACCO PLANTS INDUCED BY TAPETUM-SPECIFIC DEACETYLATION OF THE EXTERNALLY APPLIED NONTOXIC COMPOUND N-ACETYL-L-PHOSPHINOTHRICIN

A system for the inducible destruction of plant tissues based on the d eacetylation 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 remo ve the acetyl-group from N-ac-Pt giving the cytotoxic compound L-phosp hinothricin (Pt, glufosinate). Transgenic Nicotiana tabacum plants con stitutively expressing the argE gene were constructed. No effect of th e bacterial N-acetyl-L-ornithine deacetylase on plant growth and repro duction could be traced. However, application of N-ac-Pt on leaves of the transgenic plants led to the formation of necrotic areas due to th e release of Pt. Additionally, due to the uptake of the N-ac-Pt by roo ts, transgenic shoots grown on medium containing N-ac-Pt bleached with in 6-7 days and finally died. Untransformed controls showed no reactio n to high amounts of N-ac-Pt applied, either under sterile or under un sterile conditions. In order to construct inducible male-sterile plant s, the argE coding region was fused to a DNA fragment carrying sequenc es homologous to the tobacco TA29 promoter, known to function exclusiv ely in the tapetum. Owing to the tapetum-specific expression of the ch imeric 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, W ithout N-ac-Pt treatment the plants turned out to be completely fertil e making fertility restoration in the F-1 generation superflous. The s ystem presented is easy to handle and might be applicable to a wide ra nge of crop plants.