Transgenic rice plants expressing a Bacillus subtilis protoporphyrinogen oxidase gene are resistant to diphenyl ether herbicide oxyfluorfen

Protoporphyrinogen oxidase (Protox), the penultimate step enzyme of the bra nch point for the biosynthetic pathway of Chi and hemes, is the target site of action of diphenyl ether (DPE) herbicides. However, Bacillus subtilis P rotox is known to be resistant to the herbicides, In order to develop the h erbicide-resistant plants, the transgenic rice plants were generated via ex pression of B. subtilis Protox gene under ubiquitin promoter targeted to th e cytoplasm or to the plastid using Agrobacterium-mediated gene transformat ion. The integration and expression of the transgene were investigated at T o generation by DNA and RNA blots. Most transgenic rice plants revealed one copy transgene insertion into the rice genome, but some with 3 copies. The expression levels of B. subtilis Protox mRNA appeared to correlate with th e copy number. Furthermore, the plastidal transgenic lines exhibited much h igher expression of the Protox mRNA than the cytoplasmic transgenic lines. The transgenic plants expressing the B. subtilis Protox gene at To generati on were found to be resistant to oxyfluorfen when judged by cellular damage with respect to cellular leakage, Chi loss, and lipid peroxidation. The tr ansgenic rice plants targeted to the plastid exhibited higher resistance to the herbicide than the transgenic plants targeted to the cytoplasm. In add ition, possible resistance mechanisms in the transgenic plants to DPE herbi cides are discussed.