Karyotype diversity and genome size variation in Neotropical Maxillariinae orchids

Abstract

Orchidaceae is a widely distributed plant family with very diverse vegetative and floral morphology, and such variability is also reflected in their karyotypes. However, since only a low proportion of Orchidaceae has been analysed for chromosome data, greater diversity may await to be unveiled. Here we analyse both genome size (GS) and karyotype in two subtribes recently included in the broadened Maxillariinea to detect how much chromosome and GS variation there is in these groups and to evaluate which genome rearrangements are involved in the species evolution. To do so, the GS (14 species), the karyotype - based on chromosome number, heterochromatic banding and 5S and 45S rDNA localisation (18 species) - was characterised and analysed along with published data using phylogenetic approaches. The GS presented a high phylogenetic correlation and it was related to morphological groups in Bifrenaria (larger plants - higher GS). The two largest GS found among genera were caused by different mechanisms: polyploidy in Bifrenaria tyrianthina and accumulation of repetitive DNA in Scuticaria hadwenii. The chromosome number variability was caused mainly through descending dysploidy, and x=20 was estimated as the base chromosome number. Combining GS and karyotype data with molecular phylogeny, our data provide a more complete scenario of the karyotype evolution in Maxillariinae orchids, allowing us to suggest, besides dysploidy, that inversions and transposable elements as two mechanisms involved in the karyotype evolution. Such karyotype modifications could be associated with niche changes that occurred during species evolution.

Ploidy Level, Karyotype, and Genome Size of Bletilla Species (Orchidaceae) From China

“…Our information on the nuclear DNA contents of B. striata showed that the 2C values in populations with dysploidy (2n = 2x = 34; 2n = 2x = 36) were not significantly different from those in other B. striata populations with 2n = 2x = 32 (Table 1). Indeed, dysploidy events are considered the most important chromosome evolutionary mechanism in Orchidaceae (Grabiele et al, 2013;Moraes et al, 2017), and the increase from 2n = 32 to 2n = 36 in B. striata was consistent with this hypothesis. Therefore, to fully support polyploidy and dysploidy as important evolutionary mechanisms in the genus Bletilla, chromosome banding techniques and/or in situ hybridization need to be used, which will enable particular chromosome rearrangements to be tracked.…”

“…The variations in chromosome numbers also reflected frequent dysploidy events detected in Orchidaceae (Felix and Guerra, 2010;Mandakova and Lysak, 2018;Moraes et al, 2017). Dysploids with 2n = 2x = 36 and 2n = 2x = 34 in B. striata were found in this study.…”

Insights into the origin of the high variability of multivalent-meiotic associations in holocentric chromosomes of Tityus (Archaeotityus) scorpions

“…These factors may be responsible for chromosome variability, which appears to occur freely in buthids, as well as the expansion of gene families and neofunctionalization, as described by Cao et al [ 70 ] and Sharma et al [ 73 ]. Alternatively, as proposed for angiosperms [ 74 – 76 ], polyploidy/paleopolyploidy followed by repeated disploidy events also lead to the high variability of diploid numbers during meiosis I. In scorpions, however, the whole-genome duplication has been debated (for reviews, see [ 70 , 77 ]).…”

Chromosome Evolution in Connection with Repetitive Sequences and Epigenetics in Plants

“…The main factors that influence plant chromosome evolution are chromosome rearrangement and polyploidy [ 19 , 20 , 21 , 22 ]. The breakage and subsequent ligation of chromosomal segments can lead to rearrangements of the chromosome structure, such as inversions, translocations, centric split and fusion, duplications, and deletions.…”