Multicentric origin and diversification of atp6-orf79-like structures reveal mitochondrial gene flows in Oryza rufipogon and Oryza sativa.

Cytoplasmic male sterility (CMS) is a widely used genetic tool in modern hybrid rice breeding. Most genes conferring rice gametophytic CMS are homologous to orf79 and co-transcribe with atp6. However, the origin, differentiation and flow of these mitochondrial genes in wild and cultivated rice species remain unclear. In this study, we performed de novo assembly of the mitochondrial genomes of 221 common wild rice (Oryza rufipogon Griff.) and 369 Asian cultivated rice (Oryza sativa L.) accessions, and identified 16 haplotypes of atp6-orf79-like structures and 11 orf79 alleles. These homologous structures were classified into 4 distinct groups (AO-I, AO-II, AO-III and AO-IV), all of which were observed in O. rufipogon but only AO-I was detected in O. sativa, causing a decrease in the frequency of atp6-orf79-like structures from 19.9% to 8.1%. Phylogenetic and biogeographic analyses revealed that the different groups of these gametophytic CMS-related genes in O. rufipogon evolved in a multicentric pattern. The geographical origin of the atp6-orf79-like structures was further traced back, and a candidate region in north-east of Gangetic Plain on the Indian Peninsula (South Asia) was identified as the origin centre of AO-I. The orf79 alleles were detected in all three cytoplasmic types (Or-CT0, Or-CT1 and Or-CT2) of O. rufipogon, but only two alleles (orf79a and orf79b) were observed in Or-CT0 type of O. sativa, while no orf79 allele was found in other types of O. sativa. Our results also revealed that the orf79 alleles in cultivated rice originated from the wild rice population in South and South-East Asia. In addition, strong positive selection pressure was detected on the sequence variations of orf79 alleles, and a special evolutionary strategy was noted in these gametophytic CMS-related genes, suggesting that their divergence could be beneficial to their survival in evolution.

Low voltage pulse injection test of a single-stage 1 MV prototype induction voltage adder cell.

Low voltage pulse injection tests have been done on a 1 MV prototype induction cell. The tests mainly aim at measuring azimuthal uniformity of feed currents and evaluating cell electrical parameters. Tests are conducted under two cases that the cell is fed by a single pulse and two pulses, respectively. The results indicate that, in the case of the single-point feed, the best current uniformity with an azimuthal variation of 19.3% is acquired when azimuthal lines connect to cathode plates with lower half circumferences. In the case of two-pulse synchronous feed, the current uniformity becomes better, and a current with an azimuthal variation of 11.8% is achieved. Moreover, the effects of asynchronous feed on current uniformity are also experimentally investigated. The results imply that, for given injecting pulses with the duration of 70-80 ns, a time deviation less than 30 ns could be acceptable, without obvious degradation on the feed uniformity and current addition. In addition, the influences of the current uniformity and amounts of feed pulses on cell equivalent inductances are evaluated. The experiment results show that, the equivalent inductance would nearly keep a value of 130 nH as the current variation is less than 50%. However, the extreme asymmetry of feed currents or the increase of amounts of feed pulses would produce additional inductance.