Chromosomal distribution of the repetitive sequences in Zea mays and Psidium guajava, and its implications in karyotype

• Ano de defesa: 2020
• Autor(a) principal: Silva, Jéssica Coutinho
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Citogenética; Goiaba; Cariótipos; Milho; Genomas; Genética Vegetal
• Link de acesso: https://locus.ufv.br//handle/123456789/28739

Plant genomes are rich in repetitive sequences, which were initially recognized as "junk DNA". However, currently it has been demonstrated that they play important roles different processes, such as chromosomal rearrangements, gene expression and function, in addition to influencing in differences of nuclear DNA content between species. In this scenario, the identification, comparison and mapping of repetitive sequences generate evidence about the karyotype organization of plants. The present study compared karyotypes of three Zea mays accessions, by molecular cytogenetic seeking to answer if the nuclear genome size variation among them is promoted by differential amounts of repetitive sequences and/or by structural chromosomal rearrangements. Furthermore, we identify and characterize the distribution of two LTR- retrotransposons sequence in Psidium guajava karyotype. In the first study, the measurement of the nuclear DNA content of Z. mays accessions revealed a remarkable intraspecific variation from 2C = 2.00 pg to 2C = 6.10 pg. From comparative karyotypes analysis, a heterozygous terminal deletion in chromosome 3 was pointed out as a cause of lower 2C value, as well as a translocation in the short arm of chromosome 1 was observed. Differently, higher 2C value was associated with the more abundant distribution of LTR-retrotransposons from the family Grande in the karyotype. Moreover, heteromorphisms were found regarding the number and position of the 180-bp tandem repeat sequence. In the second paper, we identified and characterized two Copia LTR-retrotransposons from a genomic and chromosomal point of view in P. guajava, an economically important fruit tree. The cytogenomic analysis evidenced that these two Copia sequences, identified as RLC_Pg_1 and RLC_Pg_2, are related to the lineages RLC_egBianca_1 and RLC_egAle_2 from Eucalyptus grandis, respectively. Our work provides new insights to enlighten the role of mobile elements in diversification the P. guajava and Z. mays karyotype. Keywords: Cytogenetics. Guava. Karyotype. Maize. Plant genome. Repetitive sequences.