Identification of sex chromosome of spinach by physical mapping of 45s rDNAs by FISH

Abstract

Male and female spinach (Spinacia oleracea L, 2n = 12) were karyotyped by chromosome measurements and subjected to fluorescence in situ hybridization with 45s rDNA The chromosome complement comprised two long nearly subtelocentrics, two short subtelocentrics, two acrocentrics, and six submetacentrics.The X and Y chromosomes were not distinguished by morphological analysis; thus, six obvious 45s rDNA sites were labeled with Texas red and clearly observed as red signals on three pairs of chromosomes.Among the three pairs of signal sites, a pair of the largest one was located on the short arms of chromosome 5, which is a satellite chromosome.Another prominent signal site was found on the short arms of chromosomes 2 and 6.However, from single images with 45s rDNA (red) of male or female spinach, weak 45s rDNA sites labeled with Texas red were observed on chromosomes 1 and 3.The weak 45s rDNA signals site were located on the large arm of chromosome 3 of both male and female spinach.Interestingly, different fluorescence signals were found on chromosome 1.In male spinach, weak signals were located on the short arm of one chromosome of the largest chromosome pairs, but signals on another chromosome were not observed.In female spinach, weak signals were located on the entire short arm of largest chromosome pairs.For the first time, the largest chromosome pairs were directly identified as the sex chromosomes.The identification of these sex chromosomes is very helpful for cloning and manually locating the sex determination region of spinach.