Abstract
The two cultivated Canavalia (Adanson, 1763) species, Canavalia gladiata (N. J. von Jacquin, 1788) A. P. de Candolle, 1825 and Canavalia ensiformis (Linnaeus, 1753) A. P. de Candolle, 1825 are closely related based on morphological and molecular phylogenetic data. However, the similarities and differences in genome organization between them have not been evaluated at molecular cytogenetic level. Here, detailed karyotypes of both species were constructed using combined PI and DAPI (CPD) staining, rDNA-FISH and self-genomic in situ hybridization (sGISH). For further comparison, comparative genomic in situ hybridization (cGISH) and sequence analysis of 5S rDNA were applied. Their chromosomes were accurately identified by sGISH and rDNA-FISH signals. Both species had the karyotype formula 2n = 22 = 18m + 4m-SAT, but the karyotype of C. ensiformis was shorter and more asymmetric than that of C. gladiata. They displayed similar CPD bands at all 45S rDNA sites and centromeres. C. gladiata had ten centromeric 5S rDNA loci and two SC (secondary constriction)-associated 45S rDNA loci. C. ensiformis had nine centromeric and one interstitial 5S loci, two SC-associated and one proximal 45S loci. Their sGISH signal patterns displayed both basic similarities and distinct differences. Reciprocal cGISH generated prominent signals in all pericentromeric regions and 45S sites. There was lower level of sequence identity of the non-transcribed spacer between their 5S rDNA repeats. These data confirmed the evolutionary closeness between C. gladiata and C. ensiformis and demonstrated obvious differentiation between their genomes, and supported the opinion that C. ensiformis is more advanced in evolution than C. gladiata.
Highlights
The genus Canavalia Adanson, 1763, belonging to the tribe Diocleae of the family Fabaceae, comprises about sixty pantropical species (Smartt 1990, Snak et al 2016)
The minor fragments (459 bp and 457 bp amplified from C. gladiata and C. ensiformis, respectively) included the entire 361 bp non-transcribed spacer (NTS) or 359 bp NTS
The major fragments (940 bp and 948 bp amplified from C. gladiata and C. ensiformis, respectively) consisted of two NTS regions separated by the whole gene sequence
Summary
The genus Canavalia Adanson, 1763, belonging to the tribe Diocleae of the family Fabaceae, comprises about sixty pantropical species (Smartt 1990, Snak et al 2016). C. gladiata was domesticated in Asia and widely cultivated in the tropics whereas C. ensiformis is native to Central America and the West Indies and is widely cultivated in tropical and subtropical regions (Smartt 1990). Both are raised as food, forage, green manure, and cover crops to control erosion (Smartt 1990, Ekanayake et al 2000). The seeds of C. ensiformis are a source of concanavalin A (Morris 2007)
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