Heterochromatin banding patterns in Rutaceae‐Aurantioideae—a case of parallel chromosomal evolution

Abstract

The heterochromatin banding patterns in the karyotypes of 17 species belonging to 15 genera of Rutaceae subfamily Aurantioideae (= Citroideae) were analyzed with the fluorochromes chromomycin (CMA) and 4'-6-diamidino-2-phenylindole-2HCl (DAPI). All species were diploids, except one tetraploid (Clausena excavata) and two hexaploids [Glycosmis parviflora agg. (aggregate) and G. pentaphylla agg.]. There are only CMA/DAPI bands, including those associated with the nucleolus. Using recent cpDNA (chloroplast DNA) sequence data as a phylogenetic background, it becomes evident that generally more basal genera with rather plesiomorphic traits in their morphology, anatomy, and phytochemistry exhibit very small amounts of heterochromatin (e.g., Glycosmis, Severinia, Swinglea), whereas relatively advanced genera from different clades with more apomorphic characters display numerous large CMA bands (e.g., Merrillia, Feroniella, Fortunella). Heterochromatin increase (from 0.7 to 13.7%) is interpreted as apomorphic. The bands are mostly located in the larger chromosomes and at telomeric regions of larger arms. However, one of the largest chromosome pair has been conserved throughout the subfamily with only very little heterochromatin. The heterochromatin-rich patterns observed in different clades of Aurantioideae appear quite similar, suggesting a kind of parallel chromosomal evolution. In respect to the current classification of the subfamily, it is proposed to divide Murraya s.l. (sensu lato) into Bergera and Murraya s.s. (sensu stricto) and to place the former near Clausena into Clauseneae s.s. and the latter together with Merrillia into Citreae s.l. The subtribes recognized within Clauseneae s.s. and Citreae s.l. appear heterogeneous and should be abandoned. On the other hand, the monophyletic nature of the core group of Citrinae, i.e., the Citrus clade with Eremocitrus, Microcitrus, Clymenia, Poncirus, Fortunella, and Citrus, is well supported.

CMA Staining Analysis of Chromosomes in Citrus Relatives, Clymenia, Eremocitrus and Microcitrus

“…polyandra, M. australis, M. inodora, M. warburgiana, and Sydney hybrid were reported for the first time in this study; those of E. glauca and M. australasica have been previously reported (Guerra et al, 2000). Although the high reproducibility of CMA chromosome configuration is well known (Yamamoto, 2007), CMA banding patterns of these two species in the present study were not identical but were similar to those in studies by Guerra et al (2000). There is variability within species at least in M. australasica (Swingle and Reece, 1967).…”

“…These studies demonstrated the existence of characteristic CMA banding patterns with a high level of diversity and heterozygosity in the chromosomes of the above genera. The results also demonstrated CMA banding patterns of important species, which provide useful information on phylogenic relationships among these genera and species; however, CMA banding analysis of the other three genera has not progressed, although Guerra et al (2000) demonstrated CMA banding patterns of one species each of Eremocitrus and Microcitrus.…”

Fusion of protoplasts with irradiated microprotoplasts as a tool for radiation hybrid panel in citrus

“…(Balsamocitrinae subtribe), a distant Citrus relative, in order to better distinguish donor pieces in the receptor genome background, which would be rather difficult if closer relatives were used due to greater similarities in their genomes. Swinglea glutinosa also presents a very distinct, heterochromatin-poor karyotype, and the smallest chromosomes known in the Aurantioideae subfamily (Guerra et al, 2000).…”

Karyotype characterization of two populations of Vernonia geminata (Asteraceae, Vernonieae) using banding and FISH techniques

“…The fluorochrome DAPI preferentially stains AT-rich DNA, while CMA 3 preferentially stains GC-rich DNA. Guerra et al (2000), in studying the pattern of heterochromatic bands in Rutaceae, subfamily Aurantioideae, observed that the genus most basal in the group showed smaller amounts of heterochro-matin than did the more derived genera. Beyond fluorochrome banding, specific staining with silver nitrate or AgNOR can be used (Goodpasture and Bloom, 1975) to identify the nucleolus and chromosomes that have nucleolus organizer regions (NOR) that had been active in interphase.…”