First genome size assessment and fluorochrome chromosome banding in Argania spinosa (L.) Skeels (Sapotaceae)

Argania is a monotypic genus belonging to the family Sapotaceae and comprising the only species Argania spinosa. This taxon, endemic to southern Morocco (northern Africa), is important in arid lands. It has a high pastoral value, numerous traditional uses, and it is an important industrial crop for food and cosmetics. A few chromosome counts are available for the species but to date, there is no information on its genome size. Apart from being a parameter useful in many aspects of plant systematic and evolutionary biology, knowing the nuclear DNA amount is a pre-requisite to any genome-sequencing program. In this paper, we present for the first time data on the nuclear DNA content in Argania spinosa, from two populations, and we confirm its chromosome number. Genome size was estimated as 2C = 1.48 pg (1C = 723.72 Mbp) in both studied accessions, revealing a small genome. The chromosome count (2n = 20) revealed that the species has the lowest basic chromosome number (x = 10) in the Sapotaceae, and suggests a descending dysploidy process in the family. The first morphological characterisation of Argania spinosa's karyotype is presented here. In addition, fluorochrome banding, performed with chromomycin A(3) and DAPI, showed the absence of AT-rich regions and the presence of GC-rich regions located in three chromosome pairs, bringing the first molecular cytogenetic data in the genus.

Automated summary

Argania spinosa, a monotypic genus endemic to southern Morocco, is an important plant with high pastoral value, traditional uses, and industrial significance. This study presents the nuclear DNA content and chromosomal characteristics of this species, contributing to its molecular cytogenetics. The small genome size and unique chromosome number observed suggest a dysploidy process in the Sapotaceae family.