The smoking gun of gene transfer
Cheap football boots william MartinInstitute of Botany III, cheap football boots University of Dusseldorf, Dusseldorf, Germany. The results of that symbiosis are today’s chloroplasts, the photosynthesizing organelles of plants. One of the most important processes that occurred en route to the establishment of the chloroplast as a stably inherited organelle (as opposed to a transient endosymbiont) was the transfer of genes from the cyanobacterial symbiont’s genome to the host’s nuclear chromosomes. Recent estimates suggest that as much as 18% of the nuclear genes in Arabidopsis thaliana ultimately hypervenom phantom neymar stem from the ancestral plastid genome. But hypervenom phantom neymar gene transfer from chloroplasts to the nucleus has always been indirectly inferred from genesequence comparisons now. The fragment, which was stably integrated into the circular chloroplast chromosome by homologous recombination, contained an antibiotic resistance marker that is expressed in the chloroplast.
This allowed them to obtain plants whose plastids only their plastids homogeneously transgenic (homoplastomic transformants). Their decisive trick was then simple: in addition to the plastidspecific resistance marker, their chloroplast DNA fragment also contained a kanamycinresistance gene, which possessed a spliceosomal intron under the control of promoter specific to nuclear gene expression. These homoplastomic lines were used as the male (pollen) donor in crosses to wildtype female recipients. The resulting seed was sown on medium containing kanamycin. The expectation was that only such seedlings would survive in which the kanamycinresistance marker specific to the nuclear expression machinery had been transferred in a functional state from the chloroplast to the nuclear genome. Among 250,000 progeny tested, they found 16 independent kanamycinresistant plants (see figure) with heritable nuclear insertions of the chloroplast fragment, which in most cases segregated in a mendelian fashion. Transfers that did not encompass the region of chloroplast DNA into which the resistance gene had been inserted also went undetected. Hence, the cheap football boots true rate of bulk chloroplast DNA transfer is probably higher. On the other hand, N. tabacum is an allotetraploid, a circumstance that may buffer the potentially deleterious effects of large DNA insertions in the nuclear chromosomes, thus potentially permitting a higher transfer rate than might be expected in diploids. Yet there is no evidence one way or the other to suggest that the chloroplastderived fragments are being inserted into active genes. Given the cheap football boots geological time scales over which this rapid and efficient intracellular gene transfer mechanism has been operating, the biggest surprise of all is perhaps that there is any chloroplastspecific DNA left at all that is another story. TopFULL TEXTPrevious NextTable of contentsDownload PDFSend cheap football boots.