PubMed · 13312086
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A E PROTSENKO, A M NESTEROVA. 1955. [Cucumber white mosaic].. https://pubmed.ncbi.nlm.nih.gov/13312086/
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We used a newly synthesized allotetraploid between C. sativus (2n = 2x = 14, n gametic chromosome number, x haploid chromosome number) and C. hystrix (2n = 2x = 24) to study the genomic events in its early generations. Results from cytological characterization of the F(1) and the allotetraploid progenies showed that the rate of bivalents in meiotic metaphase I of the F(1) was greatly improved by chromosome doubling, and further improved during the selfing process of allopolyploid resulting into relatively diploid-like meiosis. Extensive genomic changes were detected by amplified fragment length polymorphism analysis. The changes mainly involved loss of parental restriction fragments and gaining of novel fragments. The total detectable changes were from 11.1 to 32.1%, and the frequency of losing parental fragments was much higher than that of gaining novel fragments. Some of the changes were initiated as early as in the F(1) hybrid, whereas others occurred after chromosome doubling (polyploid formation). No significant differences were detected in the reciprocal F(1) hybrids and S(0) generations. But the data showed that the frequency of sequence losing in C. sativus was about two times higher than in the C. hystrix. Our results demonstrated that the sequence elimination was the major event of genomic changes, and it might provide the physical basis for the diploid-like meiotic behavior in the diploidization of the newly formed allopolyploids. Moreover, the results suggest that the sequence elimination was not caused by cytoplasmic factors, and might relate to genomic recombination and to the numbers of parental chromosome.
The population diversity of progeny viruses of Kyuri green mottle mosaic virus (KGMMV) in consecutive serial passages in two systemic hosts, zucchini squash and cucumber plants, established from genetically identical viral RNA, was examined in this study. An initial plant was inoculated with in vitro transcripts from a full-length cDNA clone of KGMMV. The initial viral population (passage 0) was transferred five times in parallel populations in the same hosts species for analysis of progenies of KGMMV. The percentage of mutations of progeny viruses fluctuated slightly, as expected, during the serial passage, and these results did not correlated with the mutation frequency calculated as the total number of mutation observed in all the clones sequenced for a given viral population were divided by the total number of bases sequenced for the population. The mutation frequencies represented similar distributions over the course of serial passages in the two systemic host plants. Seventeen unique mutations were detected from a total of 40 clones (19,120 bases) sequenced, indicating a relatively small overall mutation rate of 17 nucleotide substitutions. The majority of observed mutations in the viral populations consisted of substitutions: 61.60 and 64.08% of the mutations in cucumber and zucchini populations, respectively. The types of transitions and silent mutations indicated that progenies of KGMMV reached stabilized selection during the host passages and maintained viral quasispecies in systemic hosts.
Ethylene inhibits the establishment of symbiosis between rhizobia and legumes. To examine how and when endogenous ethylene inhibits rhizobial infection and nodulation, we produced transgenic Lotus japonicus carrying the mutated melon ethylene receptor gene Cm-ERS1/H70A that confers ethylene insensitivity and fixes the transgene in the T(3) generation. The resultant transgenic plants showed reduced ethylene sensitivity because of 1-aminocyclopropane-1-carboxylate resistance and increased flowering duration, probably due to a dominant negative mechanism. When inoculated with Mesorhizobium loti, transgenic plants showed markedly higher numbers of infection threads and nodule primordia on their roots than did either wild-type or azygous plants during the early stage of cultivation period as well as during later stages, when the number of mature nodules had reached a steady state. In addition, transcripts of NIN, a gene governing infection thread formation, increased in the inoculated transgenic plants as compared with the wild-type plants. The infection responses of transgenic plants were similar to those of wild-type plants treated with ethylene inhibitors. These results imply that the endogenous ethylene in L. japonicus roots inhibits rhizobial infection at the primary nodulation, probably via NIN gene, and suggest that ethylene perception assists negative feedback regulation of secondary nodule initiation.