Cytogenetic and genomic analyses in two Erycina species

Abstract

Each species is characterized by a specific set of chromosome which is described as the chromosome portrait or karyotype The characteristics of chromosome portrait deliver precious information on genome evolution and speciation especially in related taxa with varying basic chromosome number and ploidy levels Plant karyotypes display a great diversity in number and morphology In general such a karyotype is the same for all individuals in the population An exception to that rule has been found in the orchid Erycina pusilla two different chromosome numbers (2n = 10 and 2n = 12) were reported suggesting two cytotypes E pusilla is an epiphytic Oncidiinae species native to tropical America and has been considered as a potential model organism for family Orchidaceae because of several advantageous features such as short juvenile period low chromosome number small genome size and all year round blooming To reveal the genome homology between these two cytotypes of E pusilla we generated hybrids from intercytotypic reciprocal crosses (2n = 10 × 2n = 12 and 2n = 12 × 2n = 10) and applied fluorescent staining approach genomic in situ hybridization and flow cytometry for genomic and cytogenetic analysis The parental genomes showed high similarity both in genome composition and content The hybrids displayed a chromosome number of 2n = 11 in mitotic cells Moreover five bivalents and one univalent were observed at meiotic metaphase I stage We observed meiotic synaptic behavior and found homeologous pairing with unpaired loops between parental chromosome pairing segments On the other hand we examined the karyotypic differences of parental cytotypes by means of arm ratios heterochromatin patterns as well as the presence of satellite chromosomes the number and location of rDNA and telomeric repeat sites These results demonstrate that chromosome number variation of the two cytotypes is mainly caused by extensive chromosome rearrangements not changes in genomic constitution In addition F1 hybrids between the parents with the two different chromosome numbers resulted in sterile offspring and no natural 2n = 11 cytotype population has been reported so far The combination of hybrid sterility and strikingly rearranged chromosomes supports the hypothesis that these two reported cytotypes are in fact two different species

Date of Award	2021
Original language	English
Supervisor	Song-Bin Chang (Supervisor)