Chromosome evolution in the cosmopolitan genus Lycium (Solanaceae)

Abstract

Lycium is the only member of tribe Lycieae (Solanoideae, Solanaceae), and it has a cosmopolitan distribution with its greatest diversity in southern South America, southern Africa, and southwestern North America. To date, there has been no attempt to synthesize and evaluate the significance of the available cytogenetical data from a phylogenetic perspective, which is the objective of this study. Firstly, new data on 27 taxa from all its range of distribution (FISH in all of them, banding in 23, Feulgen technique in 14) were provided to fill gaps in the information. The chromosome numbers of L. australe, L. humile, and L. repens were recorded for the first time. Species showed x = 12 with different ploidy levels (mostly diploid or tetraploid), small chromosomes, and symmetrical karyotypes. Lycium fremontii and L. repens were outstanding for having the highest numbers reported for the genus: 10x and 11x, respectively. North American species showed comparatively longer chromosomes. Secondly, cytogenetical traits were mapped on a phylogenetic tree, using character mapping and ancestral states reconstruction, to understand the dynamics of the evolutionary changes. The main cytotaxonomical features were included: chromosome number, presence of polyploidy, total length of the haploid chromosome set, mean chromosome length, karyotype formula, A 1 and A 2 asymmetry indices, percentage of heterochromatin, number of CMA + /DAPI − NORs bands, and number and position of 5S and 18S-5.8S-26S sites. The mean chromosome length, total haploid chromosome length, number of 18S-5.8S-26S loci, number of CMA + /DAPI − NORs bands underwent comparatively few transitions compared with the ploidy level and number of 5S loci. The mapping of the characters on the phylogenetic tree showed that the most probable ancestral chromosome number was 2n = 24 with several independent polyploidization events and one pair of each rDNA locus. The most likely ancestral condition for the genus would be: diploid, with small chromosomes, scarce heterochromatin, asynteny of rDNA loci, and one pair of both 18S-5.8S-26S and 5S loci.

Chromosome Evolution in the Family Solanaceae

“…is positively correlated with karyotype length (Moscone et al, 2006;Scaldaferro et al, 2013), while in others there is negative or no correlation, which is unexpected because heterochromatin is considered as an additional component of the genome (Pringle and Murray, 1993;Acosta et al, 2012Acosta et al, , 2016. Heterochromatin patterns are more variable in some genera (Jaborosa, Solanum) than in other members of the x = 12 clade (e.g., Lycium and Sclerophylax), where heterochromatin is scarce and restricted to the NORs (Lujea and Chiarini, 2017;Stiefkens et al, 2020). Variable patterns might be evidence of intense chromosomal rearrangements (Evtushenko et al, 2016) associated with diversification and colonization of new habitats, since they function as species barriers (Hughes and Hawley, 2009).…”

“…Most Solanaceae have more than half of chromosomes per complement in the m and/or sm categories. These features are useful to characterize entire clades within the family: there are groups with a majority of m chromosomes, e.g., Lycium (Stiefkens et al, 2020), but there are also groups in which complements include st and t chromosomes, e.g., Nicotiana, Capsicum, Jaborosa, Physalis (Figure 1D), Hyoscyamus, Nierembergia (Sheidai et al, 1999;Moscone et al, 2006;Scaldaferro et al, 2013;Acosta et al, 2016;Chiarini et al, 2017;Rodríguez et al, 2020) and in some clades of Solanum (Bernardello et al, 1994;Acosta et al, 2005). Some Nicotiana species have karyotypes mostly with st chromosomes (Villa, 1984) and Leptoglossis linifolia has mostly sm chromosomes (Acosta et al, 2016).…”

“…Genera with economically important species (Capsicum, Nicotiana) have received special attention (Kitamura et al, 2005;Scaldaferro et al, 2016). Within the largest genera, Lycium is the most studied (Stiefkens et al, 2020), revealing uniformity of patterns, but little is known about the rest of the family. Chromosomal rearrangements between Solanum crops and several related species have been studied using tomato and potato bacterial artificial chromosomes (BACs) in multiple FISH essays, providing support for grouping of species into sections and suggesting interspecific hybridization events (Doganlar et al, 2002;Frary et al, 2016).…”

Germplasm Resources and Strategy for Genetic Breeding of Lycium Species: A Review

“…Most of the Lycium species are diploid with 12 pairs of chromosomes (Laura et al, 2010). Some others are teraploid, octaploid, decaploid, and even hendecaploid (Bernardello et al, 1995;Stiefkens and Bernardello, 2005;Chen J. et al, 2013;Stiefkens et al, 2020;…”

Living in extreme environments: distribution of Lycium humile (Solanaceae), an endemic halophyte from the Altiplano-Puna region, South America

“… Lycium L. is the only member of tribe Lycieae ( Atropina clade, Solanaceae ; Hunziker 1977 ; Levin et al 2011 ; Särkinen et al 2013 ) and comprises nearly 90 woody species commonly found in arid, sub-arid and even saline environments ( Bernardello 2013 ). It is a cosmopolitan genus with its greatest diversity occurring in extratropical areas, in southern South America, southern Africa, and southwestern North America ( Stiefkens et al 2020 ). In South America, the shrub endemic to the Altiplano-Puna region Lycium humile Phil.…”