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The Escherichia coli ispB gene encoding octaprenyl diphosphate synthase is responsible for the synthesis of the side chain of isoprenoid quinones. We tried to construct an E. coli ispB-disrupted mutant but could not isolate the chromosomal ispB disrupted mutant unless the ispB gene or its homolog was supplied on a plasmid. The chromosomal ispB disruptants that harbored plasmids carrying the ispB homologs from Haemophilus influenzae and Synechocystis sp. strain PCC6803 produced mainly ubiquinone 7 and ubiquinone 9, respectively. Our results indicate that the function of the ispB gene is essential for normal growth and that this function can be substituted for by homologs of the ispB gene from other organisms that produce distinct forms of ubiquinone.Escherichia coli, a member of the gram-negative and facultative anaerobic group of bacteria, usually obtains energy for growth through respiration under aerobic and anaerobic conditions, in addition to energy obtained from glycolysis (8, 10). In the respiratory chain of E. coli, two types of quinones, ubiquinone 8 (UQ-8) and menaquinone 8 (MK-8), are essential components (3,5,8,10). UQ-8 is necessary for the transfer of electrons from NADH to succinate in the electron transfer system that has molecular oxygen as the final electron acceptor. MK-8 functions for the transfer of electrons from formate in the anaerobic electron transfer system which uses nitrate as the final electron acceptor. While E. coli has both UQ-8 and MK-8, some microorganisms contain only one type of quinone; e.g., Bacillus species produce only MK and Acetobacter species generally produces only UQ (3, 5). Why does E. coli synthesize two kinds of quinones when other bacteria can subsist on only one? To address this question, mutants defective in the synthesis of UQ, MK, or both have been isolated (19). ubi and men mutants are respiration defective under aerobic and anaerobic conditions, respectively (10,19,20). A strain defective in both ubi and men has been constructed and found to grow very slowly (19). However, it appears likely that the ubi mutation was leaky in this strain, as a small amount of UQ could still be detected (19). We have taken a different approach by isolating a mutant with a deletion of the ispB gene, which encodes octaprenyl diphosphate synthase (1). This enzyme is responsible for the synthesis of the side chain of both UQ and MK, and strains defective in this enzyme should not be able to synthesize active forms of UQ or MK (1). However, we found that it was impossible to obtain an ispB deletion mutant unless the ispB gene or its homolog was supplied on a plasmid. Thus, we suggest that the ispB gene is essential for the normal growth of E. coli.Construction of an ispB-disrupted mutant. To investigate the function of the ispB gene, a plasmid (pTC2) used to disrupt this gene was constructed by inserting the chloramphenicol acetyltransferase (cat) gene into the ispB gene (Fig. 1). We attempted to obtain chloramphenicol-resistant strains by transforming strain FS1576 (recD) (15) wit...

SummaryWe identified the Magnaporthe oryzae avirulence effector AvrPi9 cognate to rice blast resistance gene Pi9 by comparative genomics of requisite strains derived from a sequential planting method.AvrPi9 encodes a small secreted protein that appears to localize in the biotrophic interfacial complex and is translocated to the host cell during rice infection. AvrPi9 forms a tandem gene array with its paralogue proximal to centromeric region of chromosome 7. AvrPi9 is expressed highly at early stages during initiation of blast disease.Virulent isolate strains contain Mg-SINE within the AvrPi9 coding sequence. Loss of AvrPi9 did not lead to any discernible defects during growth or pathogenesis in M. oryzae. This study reiterates the role of diverse transposable elements as off-switch agents in acquisition of gainof-virulence in the rice blast fungus.The prevalence of AvrPi9 correlates well with the avirulence pathotype in diverse blast isolates from the Philippines and China, thus supporting the broad-spectrum resistance conferred by Pi9 in different rice growing areas. Our results revealed that Pi9 and Piz-t at the Pi2/9 locus activate race specific resistance by recognizing sequence-unrelated AvrPi9 and AvrPiz-t genes, respectively.

Many mule duck and Cherry Valley duck flocks in different duck-producing regions of China have shown signs of an apparently new disease designated "short beak and dwarfism syndrome" (SBDS) since 2015. The disease is characterized by dyspraxia, weight loss, a protruding tongue, and high morbidity and low mortality rates. In order to characterize the etiological agent, a virus designated SBDSV M15 was isolated from allantoic fluid of dead embryos following serial passage in duck embryos. This virus causes a cytopathic effect in duck embryo fibroblast (DEF) cells. Using monoclonal antibody diagnostic assays, the SBDSV M15 isolate was positive for the antigen of goose parvovirus but not Muscovy duck parvovirus. A 348-bp (2604-2951) VP1gene fragment was amplified, and its sequence indicated that the virus was most closely related to a Hungarian GPV strain that was also isolated from mule ducks with SBDS disease. A similar disease was reproduced by inoculating birds with SBDSV M15. Together, these data indicate that SBDSV M15 is a GPV-related parvovirus causing SBDS disease and that it is divergent from classical GPV isolates.