Cytogenetic characterization and karyotype evolution in six Macroptilium species (Leguminosae)

Abstract

Macroptilium (Benth.) Urb. is a neotropical legume genus from the subtribe Phaseolinae. The investigated species present a stable chromosome number (2n = 22), but differ in their karyotype formulae, suggesting the presence of chromosome rearrangements. In this work, we comparatively analysed the karyotypes of six species (M. atropurpureum, M. bracteatum, M. erythroloma, M. gracile, M. lathyroides and M. martii) from the two main clades that form the genus. Heterochromatin distribution was investigated with CMA/DAPI staining and fluorescent in situ hybridization (FISH) was used to localise the 5S and 35S ribosomal DNA (rDNA) sites. Single copy BACs (Bacterial Artificial Chromosomes) previously mapped in the related genera Phaseolus L. and Vigna Savi were used to establish chromosome orthologies and to investigate possible rearrangements among species. CMA+/DAPI- bands were observed, mostly associated with rDNA sites. Additional weak, pericentromeric bands were observed on several chromosomes. Although karyotypes were similar, species could be differentiated mainly by the number and position of the 5S and 35S rDNA sites. BAC markers demonstrated conserved synteny of the main rDNA sites on orthologous chromosomes 6 and 10, as previously observed for Phaseolus and Vigna. The karyotypes of the six species could be differentiated, shedding light on its karyotype evolution.

Karyotype Description and Comparative Chromosomal Mapping of 5S rDNA in 21 species

“…Overall, 5S rDNA occurred in at least two chromosomes in all 64 plants. With advances in science and technology, the occurrence of 5S rDNA has been confirmed in an increasing amount of species (de Barros et al 2023, de Moraes et al 2023, Kroupin et al 2023, Rodríguez-González et al 2023). Whether the reported length of 5S rDNA is a complete or partial sequence, there is no doubt there is a big difference among these 5S rDNA, including the length and base pair (Röser et al 2001, Kulak et al 2002, Moraes et al 2022).…”

“…After comparing the 5S rDNA in previous studies and in ours, both perfectly reflect the extensive diversity in P. nepalensis , which can distinguish all 18 chromosomes according to the signal position, signal intensity, and signal number. Nevertheless, 5S rDNA was quite conserved and dormant in numerous species, such as C. campanulatus , C. sativa , H. rhamnoides , J. regia , M. atropurpureum , P. stratiotes , P. trichocarpa , and Sanguisorba L. (Mishima et al 2002, Luo and Chen 2019, 2020, Xin et al 2020, Alexandrov et al 2022, Luo et al 2022a, Stepanenko et al 2022, de Barros et al 2023). Why is there such a big difference in 5S rDNA among the above species?…”

“…The lengths of the 5S rDNA sequence ranged from 48 bp (Turner et al 2005) to 854 bp (Liu et al 2017) because of its high copies and variations when searching for “5S rDNA” in the database Nucleotide of National Center for Biotechnology Information. Furthermore, the lengths of 5S rDNA as a FISH probe in the PubMed database from NCBI varied considerably: 41 bp (Luo et al 2017, Islam-Faridi et al 2020), 94 bp (Sergeeva et al 2017), 117 bp (Lukjanová et al 2023), 120 bp (Taketa et al 2001, Symonová et al 2017, Deon et al 2022, de Moraes et al 2023), 124 bp (Waminal et al 2018), 131 bp (Sergeeva et al 2017), 222 bp (Glugoski et al 2018), 285 bp (Röser et al 2001), 300 bp (Araya-Jaime et al 2022), 302 bp (Zhang et al2016), 303 bp (Mahelka et al 2013), 320 bp (Khensuwan et al 2023), 324 bp (Kamisugi et al 1994), 326 bp (Robledo and Seijo 2008), 329 bp (Röser et al 2001), 347 bp, ∼400 bp (Pedrosa et al 2002), 410 bp (Kovács et al 2023), 456 bp (Röser et al 2001), 468 bp, 473 bp, 477 bp, 496 bp (Martins et al 2000), 497 bp (Alexandrov et al 2022), 498 bp (Martins et al 2000), 500 bp (de Barros et al 2023), 556 bp (Gottlob-McHugh et al 1990), 596 bp (Joshi et al 2023), 702 bp (Glugoski et al 2018), 871 bp (Amarasinghe and Carlson 1988), and 1193 bp (Glugoski et al 2020).…”

“…The 5S rDNA signal has been found in the chromosome interstitial position from Macroptilium bracteatum (Nees & Mart.) Maréchal & Baudet (de Barros et al 2023), Deschampsia antarctica E. Desv (Amosova et al 2022), Polemonium caeruleum Linnaeus (Samatadze et al 2023), in the chromosome distal position from Pinus koraiensis Siebold et Zuccarini (Cai et al 2006), Cannabis sativa L. (Alexandrov et al 2022), Pseudotsuga menziesii (Mlrb.) Franco (Amarasinghe and Carlson 1988), or in the chromosome proximal position from Brassica rapa L. (Campomayor et al 2021), even as far away the chromosome from Hedysarum setigerum Turcz.…”

Cytogenomic and phylogenomic evidence for new infrageneric relationships in Macroptilium (Benth.) beans

“…Six cytogenetically analysed species ( ve from section A and one from section B) showed the same chromosome number 2n = 22, similar to observed for most Phaseolus, Vigna and other Phaseoleae species (de Barros et al 2023). However, variation in number and location of 5S and 35S rDNA sites was observed within and between the sections, including intraspeci c variation in 5S rDNA sites among M. gracile individuals (de Barros et al 2023). In this sense, additional cytogenomic analyses could improve our understanding of the chromosomal evolution within Phaseoleae, as well as give additional support for the two sections of Macroptillium.…”