Carrot is one of the most important vegetables worldwide, owing to its capability to develop fleshy, highly nutritious storage roots. It was domesticated ca. 1,100 years ago in Central Asia. No systematic knowledge about the molecular mechanisms involved in the domestication syndrome in carrot are available, however, the ability to form a storage root is undoubtedly the essential transition from the wild Daucus carota to the cultivated carrot. Here, we expand on the results of a previous study which identified a polymorphism showing a significant signature for selection upon domestication. We mapped the region under selection to the distal portion of the long arm of carrot chromosome 2, confirmed that it had been selected, as reflected in both the lower nucleotide diversity in the cultivated gene pool, as compared to the wild (πw/πc = 7.4 vs. 1.06 for the whole genome), and the high FST (0.52 vs. 0.12 for the whole genome). We delimited the region to ca. 37 kb in length and identified a candidate domestication syndrome gene carrying three non-synonymous single nucleotide polymorphisms and one indel systematically differentiating the wild and the cultivated accessions. This gene, DcAHLc1, belongs to the AT-hook motif nuclear localized (AHL) family of plant regulatory genes which are involved in the regulation of organ development, including root tissue patterning. AHL genes work through direct interactions with other AHL family proteins and a range of other proteins that require intercellular protein movement. Based on QTL data on root thickening we speculate that DcAHLc1 might be involved in the development of the carrot storage root, as the localization of the gene overlapped with one of the QTLs. According to haplotype information we propose that the ‘cultivated’ variant of DcAHLc1 has been selected from wild Central Asian carrot populations upon domestication and it is highly predominant in the western cultivated carrot gene pool. However, some primitive eastern landraces and the derived B7262 purple inbred line still carry the ‘wild’ variant, reflecting a likely complexity of the genetic determination of the formation of carrot storage roots.

The parasitic genus Cuscuta (Convolvulaceae) is exceptional among plants with respect to centromere organization, including both monocentric and holocentric chromosomes, and substantial variation in genome size and chromosome number. We investigated 12 species representing the diversity of the genus in a phylogenetic context to reveal the molecular and evolutionary processes leading to diversification of their genomes. We measured genome sizes and investigated karyotypes and centromere organization using molecular cytogenetic techniques. We also performed low-pass whole genome sequencing and comparative analysis of repetitive DNA composition. A remarkable 102-fold variation in genome sizes (342-34 734 Mbp/1C) was detected for monocentric Cuscuta species, while genomes of holocentric species were of moderate sizes (533-1545 Mbp/1C). The genome size variation was primarily driven by the differential accumulation of LTR-retrotransposons and satellite DNA. The transition to holocentric chromosomes in the subgenus Cuscuta was associated with loss of histone H2A phosphorylation and elimination of centromeric retrotransposons. In addition, basic chromosome number of holocentric species (x = 7) was smaller than in monocentrics (x = 15 or 16). We demonstrated that the transition to holocentricity in Cuscuta was accompanied by significant changes in epigenetic marks, chromosome number and the repetitive DNA sequence composition.

The prevalence of non-autonomous class II transposable elements (TEs) in plant genomes may serve as a tool for relatively rapid and low-cost development of gene-associated molecular markers. Miniature inverted-repeat transposable element (MITE) copies inserted within introns can be exploited as potential intron length polymorphism (ILP) markers. ILPs can be detected by PCR with primers anchored in exon sequences flanking the target introns. Here, we designed primers for 209 DcSto (Daucus carota Stowaway-like) MITE insertion sites within introns along the carrot genome and validated them as candidate ILP markers in order to develop a set of markers for genotyping the carrot. As a proof of concept, 90 biallelic DcS-ILP markers were selected and used to assess genetic diversity of 27 accessions comprising wild Daucus carota and cultivated carrot of different root shape. The number of effective alleles was 1.56, mean polymorphism informative content was 0.27, while the average observed and expected heterozygosity was 0.24 and 0.34, respectively. Sixty-seven loci showed positive values of Wright's fixation index. Using Bayesian approach, two clusters comprising four wild and 23 cultivated accessions, respectively, were distinguished. Within the cultivated carrot gene pool, four subclusters representing accessions from Chantenay, Danvers, Imperator, and Paris Market types were revealed. It is the first molecular evidence for root-type associated diversity structure in western cultivated carrot. DcS-ILPs detected substantial genetic diversity among the studied accessions and, showing considerable discrimination power, may be exploited as a tool for germplasm characterization and analysis of genome relationships. The developed set of DcS-ILP markers is an easily accessible molecular marker genotyping system based on TE insertion polymorphism.