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Sugarcane genome architecture decrypted with chromosome-specific oligo probes

Piperidis N., D'Hont A.. 2020. Plant Journal : 13 p..

Sugarcane (Saccharum spp.) is probably the crop with the most complex genome. Modern cultivars (2n = 100¿120) are highly polyploids and aneuploids derived from interspecific hybridization between Saccharum officinarum (2n = 80) and Saccharum spontaneum (2n = 40¿128). Chromosome-specific oligonucleotide probes were used in combination with genomic in situ hybridization to analyze the genome architecture of modern cultivars and representatives of their parental species. The results validated a basic chromosome number of x = 10 for S. officinarum . In S. spontaneum , rearrangements occurred from a basic chromosome of x = 10, probably in the Northern part of India, in two steps leading to x = 9 and then x = 8. Each step involved three chromosomes that were rearranged into two. Further polyploidization led to the wide geographical extension of clones with x = 8. We showed that the S. spontaneum contribution to modern cultivars originated from cytotypes with x = 8 and varied in proportion between cultivars (13¿20%). Modern cultivars had mainly 12 copies for each of the first four basic chromosomes, and a more variable number for those basic chromosomes whose structure differs between the two parental species. One-four of these copies corresponded to entire S. spontaneum chromosomes or interspecific recombinant chromosomes. In addition, a few inter-chromosome translocations were revealed. The new information and cytogenetic tools described in this study substantially improve our understanding of the extreme level of complexity of modern sugarcane cultivar genomes.

Thématique : Génétique et amélioration des plantes

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