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The structure of repetitive sequences of the JNK block present in the pericentromeric region of the 2RL chromosome was studied in Secale vavilovii. Amplification of sequences present between the JNK sequences led to the identification of seven abnormal DNA fragments. Two of these fragments showed high similarity to the glutamate 5-kinase gene and putative alcohol dehydrogenase gene of trypanosomatid from the genus Leishmania, whose presence can be explained by horizontal gene transfer (HGT). Other fragments were similar to mitochondrial gene for ribosomal protein S4 in plants and to the glycoprotein (G) gene of the IHNV virus. Presumably, they are pseudogenes inserted into the JNK heterochromatin region. Within this region, also fragments similar to the rye repetitive sequence and chromosome 3B in wheat were found. There is no known mechanism that would explain how foreign sequences were inserted into the block region of tandem repetitive sequences of the JNK family.
Employing FISH analysis as well as BLAST and CUSTAL W (1.82) programs, we investigated types of DNA nucleotide sequences building an additional heterochromatic band in 2R chromosomes of 3 lines of Secale vavilovii Grossh. The probes used in FISH analysis were designed based on the reverse transcriptase sequence of Ty 1-copia and Ту 3-gypsy retrotransposons and the 5S rRNA gene sequence. No hybridization signals from the reverse transcriptase probes were observed in the chromosome region where the additional band occurs. On the other hand, signals were observed after hybridization with the 5S rDNA probe, clearly suggesting the presence of that type of sequences in the analyzed heterochromatin band. Using BLAST and CUSTAL W programs, we revealed high similarity of the JNK1 sequence to the 5S rRNA gene from Hordeum chilense (HCH1016, HCH1018, 88%) and to a fragment of the 5S rRNA sequence of H. marinum (HMAR003, 97%). In addition, the same fragment of JNK1 was shown to be very similar to the part of the Angela retrotransposon (92%) as well as to the SNAC 426K20-1 transposon (89%) belonging to CACTA family, both from Triticum monococcum, and to Zingeria biebersteiniana pericentromeric sequences (78%). The similarity of JNK1 to those sequences may be accidental or the JNK1 may represent an ancient mobile genetic element that caught the 5S rRNA sequence. During the evolution those sequences might have been accumulated in the particular region on the 2R chromosome. Our results suggest that the additional heterochromatin band in chromosomes 2R of S. vavilovii is a collection of defective genes and/or mobile genetic elements.
The paper reports chromosome numbers for 13 taxa of Elatine L., including all 11 species occurring in Europe, namely E. alsinastrum, E. ambigua, E. brachysperma, E. brochonii, E. californica, E. campylosperma, E. gussonei, E. hexandra, E. hungarica, E. hydropiper, E. macropoda, E. orthosperma, E. triandra originating from 17, field-collected populations. For seven of them (E. ambigua, E. californica, E. campylosperma, E. brachysperma, E. brochonii, E. hungarica, E. orthosperma) the chromosome numbers are reported for the first time. With these records, chromosome numbers for the whole section Elatinella Seub. became available. Although 2n = 36 was reported to be the most common and the lowest chromosome number in the genus, our data show that out of thirteen species analyzed, six had 36 chromosomes but five species had 54 chromosomes, and the lowest number of chromosomes was 18. These data further corroborates that the basic chromosome number in Elatine is x = 9.
Plants are continuously exposed to various environmental stresses and they respond to them in different ways. Ambient temperature is among the most important environmental cues that directly influence plant growth and yield. Research in recent years has revealed that epigenetic mechanisms play a key role in plants' response to temperature stress. Changes in gene expression evoked by stress signals follow post-translational histone modifications, DNA methylation, histone variant incorporation, and the action of chromatin remodeling factors and Polycomb group proteins. The majority of epigenetic modifications induced by temperature stress are reversible in nature; thus, chromatin returns to its previous state after the stress has passed. Some modifications seem stable, however, due presumably to so-called stress memory. Epigenetic modifications can be inherited through mitosis and meiosis. By dint of epigenetic memory, plants can more efficiently respond to future stressful conditions, thereby increasing their potential for environmental adaptation. Recognition of the epigenetic mechanisms that take part in plants' response to changes of ambient temperature will increase our understanding of adaptations to stress conditions.
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