The cytohistological basis of apospory in Hypericum perforatum L.

St. John's wort (Hypericum perforatum L., 2n = 4x = 32) is a medicinal plant that produces pharmaceutically important metabolites with antidepressive, anticancer and antiviral activities. It is also regarded as a serious weed in many countries. H. perforatum is furthermore an attractive model system for the study of apomixis. Natural populations of H. perforatum are predominantly composed of tetraploid individuals, although diploids and hexaploids are known to occur. It has been demonstrated that while diploids are sexual, polyploids are facultative apomictic whereby a single individual can produce both sexual and apomictic seeds. Despite our increasing understanding of gamete formation in sexually reproducing species, relatively little is known regarding the cytological basis of reproduction in H. perforatum. Here, we have studied embryo sac formation and the genetic constitution of seeds by means of staining-clearing of ovules/ovaries, DIC microscopy and flow cytometric seed screening (FCSS) of embryo and endosperm DNA contents. Comparisons of female sporogenesis and gametogenesis between sexual and apomictic accessions have enabled the identification of major phenotypic differences in embryo sac formation, in addition to complex fertilization scenarios entailing reduced and unreduced male and female gametes. These data provide new insights into the production of aposporous seeds in H. perforatum, and complement ongoing population genetic, genomic and transcriptomic studies.

Transcription of LINE-derived sequences in exercise-induced stress in horses.

A large proportion of mammalian genomes is represented by transposable elements (TE), most of them being long interspersed nuclear elements 1 (LINE-1 or L1). An increased expression of LINE-1 elements may play an important role in cellular stress-related conditions exerting drastic effects on the mammalian transcriptome. To understand the impact of TE on the known horse transcriptome, we masked the horse EST database, pointing out that the amount is consistent with other major vertebrates. A previously developed transcript-derived fragments (TDFs) dataset, deriving from exercise-stimulated horse peripheral blood mononuclear cells (PBMCs), was found to be enriched with L1 (26.8% in terms of bp). We investigated the involvement of TDFs in exercise-induced stress through bioinformatics and gene expression analysis. Results indicate that LINE-derived sequences are not only highly but also differentially expressed during physical effort, hinting at interesting scenarios in the regulation of gene expression in relation to exercise.