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The expression level of HaCRE1, a sunflower long-terminal-repeats retrotransposon which was shown to be inserted into the genome in relatively recent times was studied in detail in order to evaluate its mutagenic potential. A meta-analysis was performed, using cDNA libraries available from public repositories including cDNA sequences isolated from roots of sunflower plants treated with different plant hormones, NaCl and polyethylene glycol. HaCRE1 was expressed at low level under all treatments and even in the control roots, compared to sunflower gene sequences. Only abscisic acid treatment induced over-expression of the retrotransposon. The putative cis-regulatory sequences responsible for HaCRE1 transcription were identified in its 5'-long-terminalrepeat. It was concluded that, even at low level, this still "young" retrotransposon maintains its capacity to transpose and hence its mutagenic potential. [ABSTRACT FROM AUTHOR]

Seagrasses as Posidonia oceanica reproduce mostly by vegetative propagation, which can reduce genetic variability within populations. Since, in clonally propagated species, insurgence of genetic variability can be determined by the activity of transposable elements, we have estimated the activity of such repeat elements by measuring their expression level in the leaves of plants from a Mediterranean site, for which Illumina complementary DNA (cDNA) sequence reads (produced from RNAs isolated by leaves of plants from deep and shallow meadows) were publicly available. Firstly, we produced a collection of retrotransposon-related sequences and then mapped Illumina cDNA reads onto these sequences. With this approach, it was evident that Posidonia retrotransposons are, in general, barely expressed; only nine elements resulted transcribed at levels comparable with those of reference genes encoding tubulins and actins. Differences in transcript abundance were observed according to the superfamily and the lineage to which the retrotransposons belonged. Only small differences were observed between retrotransposon expression levels in leaves of shallow and deep Posidonia meadow stands, whereas one TAR/Tork element resulted differentially expressed in deep plants exposed to heat. It can be concluded that, in P. oceanica, the contribution of retrotransposon activity to genetic variability is reduced, although the nine specific active elements could actually produce new structural variations. [ABSTRACT FROM AUTHOR]