Development of Chromosome Genomics in Saffron

Crocus sativus L. (saffron crocus) is a monocot herbaceous species of the Iridaceae family grown in the Mediterranean Basin and Western Asia. The plant is a source of spice saffron, the most expensive spice by weight, with a variety of uses apart from cooking. The spice is obtained from dried stigmas of flowers and marketed as saffron filaments, or powder from milled stigmas. Saffron crocus is a genetically monomorphic clone propagated vegetatively and its sterility has been attributed to its triploidy (2n=3x=24). To date, only a few genetic diversity studies have been completed and the knowledge of saffron crocus genome organization remains poor. In order to facilitate the analysis of the huge (10.64 Gb) and polypoid genome, we have developed a chromosome-based strategy, which relies on dissecting the genome to single chromosomes. During the work, liquid suspensions of intact mitotic chromosomes were prepared from synchronized root tips of hydroponically grown bulbs. The chromosomes in suspension were stained by DAPI and analyzed by flow cytometry. Flow karyotypes thus obtained indicated that a majority of chromosomes could be flow-sorted only in groups of two or more. In order to overcome this difficulty, single copies of chromosomes are flow-sorted, their DNA amplified and sequenced to obtain chromosome-specific sequences. The chromosome-based strategy we have developed for saffron crocus not only reduces sample complexity prior to DNA sequencing, but avoids problem due the presence of three highly similar genomes. The work is in progress to sequence all chromosomes of saffron crocus using illumina technology