Comparative study of the 5S rDNA non-transcribed spacers in Lunario and Rosso varieties of Citrus limon (L.) Burm. f.

Lemon (Citrus limon (L.) Burm. f.) is a fruit plant that is widely grown in India and other countries with subtropical climates. The agricultural significance of lemon largely determines the high scientific interest in studying its genome. Such part of a genome as ribosomal DNA (rDNA) is often studied by geneticists with theoretical and applied purposes. In this work, sixteen non-transcribed spacers of the lemon 5S rDNA (8 from Lunario and 8 from Rosso varieties) were amplified with the universal 5S1/5S2 primers, purified, cloned in AT-vector, and sequenced. These sequences were processed, aligned and characterized for length, presence of mutations and distribution of different DNA motifs. Seven NTSs of the Lunario variety were 105 bp in length, and the eighth NTS was 77 bp because a large deletion was found in its start part. Five NTSs of the Rosso variety were 218 bp, two – 216 bp, and one – 185 bp in length. This short NTS has a 31 bp deletion in the middle part of the sequence. The emergence of typical 105 bp lemon NTSs from longer NTSs due to deletion has been suggested. The start-motif analysis and the search for poly-T, poly-C, poly-G and TATA-like motifs were carried out in the sequenced NTSs. Based on the obtained results, conclusions were made about the role of the CTCTTTT, CGCCGG, and GCGGC motifs in the appearance of deletions. Also, the results shed more light on the question of the origin of the Rosso variety. The knowledge obtained can be useful in the selection process involving lemon varieties and an analysis of citrus hybrids.