Cytogenetic analysis of Citrus Linnaeus, 1753 species is complicated by the small size and morphological similarity of their chromosomes. In this study, we applied the fluorescence in situ hybridization (FISH) method using rDNA probes, as well as newly developed oligonucleotide probes based on previously uncharacterized tandem repeats identified in citrus genomes. Four tandem repeats (CL1, CL14, CL262, and CL122) were mapped to the chromosomes of five Citrus species: Citrus medica Linnaeus, 1753, Citrus × aurantiifolia (Christmann, 1777) Swingle, 1913, Citrus × limon (Linnaeus, 1753) Osbeck, 1765, Citrus myrtifolia Rafinesque, 1838, and Citrus × latifolia Tanaka, 1951. The repeats exhibited distinct and partially species-specific distribution patterns: CL1 was detected in all species, whereas CL262, CL122, and CL14 exhibited more restricted localization. A comparative analysis of their chromosomal distribution in relation to 45S- and 5S-rDNA loci revealed differences between the conserved regions of ribosomal DNA and the more dynamic tandem repeats. The identified repeats represent useful cytogenetic markers for chromosome identification, karyotyping, and comparative analysis within the genus Citrus .

In our study, we analyzed the repeatomes of 12 Citrus plants, including 4 ancestral species and 8 the most widespread cultivated species. We detected an atypically high content of “Athila” and “Sire” LTR retrotransposons for angiosperms. For these plants, phylogenetic trees were constructed based on the nuclear repeatome, plastome, and 35S rDNA cistron, using sequencing data from open databases and, for the first time, sequencing data from our collection. The analysis demonstrated that the plastome carries a strong phylogenetic signal, which is most consistent with the updated classification of the Citrus genus, showing a distinct pattern compared to the other two phylogenetic trees.

In the context of climate change and the need to reduce pesticide and agrochemical use, the development of sustainable crops is becoming increasingly important. Epigenetic mechanisms, such as histone modifications, allow plants to adapt to stress without altering their DNA sequence. Histone demethylases are of particular interest as enzymes that activate defense genes. Concurrently, circular RNAs (circRNAs) have emerged as a new class of regulatory molecules capable of modulating gene expression. The aim of this study was to identify and validate circRNAs derived from histone demethylase genes in maize (Zea mays L.) during early developmental stages. The research was conducted on 10-day-old seedlings. Based on annotated genes and the PlantcircBase 7.0 database, six predicted circRNAs were selected. They were validated using PCR with divergent primers and subsequent sequencing. The formation of only one circular RNA out of the six predicted was experimentally confirmed – from the locus of the demethylase gene Zm00001d051961. It has been established that this circRNA is formed through backsplicing between the 2nd and the 7th exons, is 2016 nucleotides in size, and exhibits tissue-specific expression, predominantly in the leaves. This is the first experimental proof of a circRNA originating from a histone demethylase gene locus in maize. The discovered tissue-specific expression suggests that this circRNA may be involved in the fine-tuning of the demethylase's activity, potentially influencing the epigenetic status of chromatin. This discovery enhances the understanding of plant epigenetic plasticity and lays the groundwork for developing new breeding strategies aimed at enhancing crop stress resilience.