TI PLASMID-ENCODED GENES RESPONSIBLE FOR CATABOLISM OF THE CROWN GALLOPINE MANNOPINE BY AGROBACTERIUM-TUMEFACIENS ARE HOMOLOGS OF THE T-REGION GENES RESPONSIBLE FOR SYNTHESIS OF THIS OPINE BY THE PLANT TUMOR

Agrobacterium tumefaciens NT1 harboring pSaB4, which contains the 14-k b BamHI fragment 4 from the octopine/mannityl opine-type Ti plasmid pT i15955, grew well with agropine (AGR) but slowly with mannopine (MOP) as the sole carbon source. When a second plasmid encoding a dedicated transport system for MOP was introduced, these cells grew well with bo th AGR and MOP. Transposon insertion mutagenesis and subcloning identi fied a 5.7-kb region of BamHI fragment 4 that encodes functions requir ed for the degradation of MOP. DNA sequence analysis revealed seven pu tative genes in this region:mocD (moc for mannityl opine catabolism) a nd mocE, oriented from right to left, and mocRCBAS, oriented from left to right. Significant identities exist at the nucleotide and derived amino acid sequence levels between these moc genes and the mas genes t hat are responsible for opine biosynthesis in crown gall tumors. MocD is a homolog of Mas2, the anabolic conjugase encoded by mas2'. MocE an d MocC are related to the amino half and the carboxyl half, respective ly, of Mas1 (MOP reductase), the second enzyme for MOP biosynthesis. T hese results indicate that the moc and mns genes evolved from a common origin. MocR and MocS are related to each other and to a putative rep ressor for the AGR degradation system encoded by the rhizogenic plasmi d pRiA4. MocB and MocA are homologs of 6-phosphogluconate dehydratase and glucose-6-phosphate dehydrogenase, respectively. Mutations in mocD and mocE but not mocC, are suppressed by functions encoded by the chr omosome or the 450-kb megaplasmid present in many Agrobacterium isolat es. We propose that moc genes derived from genes located elsewhere in the bacterial genome and that the tumor-expressed mas genes evolved fr om the bacterial moc genes.