Molecular and functional characterization of cDNA encoding fructan:fructan 6G-fructosyltransferase (6G-FFT)/ fructan:fructan 1-fructosyltransferase (1-FFT) from perennial ryegrass (Lolium perenne L.).

International audienceFructans are the main storage compound in Lolium perenne. To account for the prevailing neokestose-based fructan synthesis in this species, a cDNA library of L. perenne was screened by using the onion (Allium cepa) fructan:fructan 6G-fructosyltransferase (6G-FFT) as a probe. A full length Lp6G-FFT clone was isolated with significant homologies to vacuolar type fructosyltransferases and invertases. The functionality of the cDNA was tested by heterologous expression in Pichia pastoris. The recombinant protein demonstrated both 6G-FFT and fructan:fructan 1-fructosyltransferase activities (1-FFT) with a maximum 6G-FFT/1-FFT ratio of two. The activity of 6G-FFT was investigated with respect to developmental stage, tissue distribution, and alterations in carbohydrate status expression and compared to sucrose:sucrose 1-fructosyltransferase (1-SST). Lp6G-FFT and Lp1-SST were predominantly expressed in the basal part of elongating leaves and leaf sheaths. Expression of both genes declined along the leaf axis, in parallel with the spatial occurrence of fructan and fructosyltransferase activities. Surprisingly, Lp6G-FFT was highly expressed in photosynthetically active tissues where very low extractable fructosyltransferase activity and fructan amounts were detected, suggesting a post-transcriptional regulation of expression. Lp6G-FFT gene expression increased only in elongating leaves following similar increases of sucrose content in blades, sheaths, and elongating leaf bases. Regulation of Lp6G-FFT gene expression depends on the tissue according to its sink-source status

Genomic and proteomic analyses indicate that banchine and campoplegine polydnaviruses have similar, if not identical, viral ancestors

International audiencePolydnaviruses form a group of unconventional double-stranded DNA (dsDNA) viruses transmitted by endoparasitic wasps during egg laying into caterpillar hosts, where viral gene expression is essential to immature wasp survival. A copy of the viral genome is present in wasp chromosomes, thus ensuring vertical transmission. Polydnaviruses comprise two taxa, Bracovirus and Ichnovirus, shown to have distinct viral ancestors whose genomes were "captured" by ancestral wasps. While evidence indicates that bracoviruses derive from a nudivirus ancestor, the identity of the ichnovirus progenitor remains unknown. In addition, ichnoviruses are found in two ichneumonid wasp subfamilies, Campopleginae and Banchinae, where they constitute morphologically and genomically different virus types. To address the question of whether these two ichnovirus subgroups have distinct ancestors, we used genomic, proteomic, and transcriptomic analyses to characterize particle proteins of the banchine Glypta fumiferanae ichnovirus and the genes encoding them. Several proteins were found to be homologous to those identified earlier for campoplegine ichnoviruses while the corresponding genes were located in clusters of the wasp genome similar to those observed previously in a campoplegine wasp. However, for the first time in a polydnavirus system, these clusters also revealed sequences encoding enzymes presumed to form the replicative machinery of the progenitor virus and observed to be overexpressed in the virogenic tissue. Homology searches pointed to nucleocytoplasmic large DNA viruses as the likely source of these genes. These data, along with an analysis of the chromosomal form of five viral genome segments, provide clear evidence for the relatedness of the banchine and campoplegine ichnovirus ancestors