Construction of methylation linkage map based on MSAP and SSR markers in Sorghum bicolor (L.)

Sorghum [Sorghum bicolor (L.) Moench] is one of the most important crops in the semiarid regions of the world. A methylation genetic linkage map of sorghum was constructed using a F2 population derived from a cross of B(2)V(4) x 1383-2 based on methylation-sensitive amplified polymorphism (MSAP) and simple sequence repeats (SSR) markers. The map including 11 linkage groups was constructed with 151 loci covering 483.6 cM, 122 of them were MSAP markers, of which 89 loci were produced from EcoRI/MspI enzyme digestion, and 33 loci were produced from EcoRI/HpaII enzyme digestion. The average and maximal distances between adjacent two individual markers were 3.2 and 22.7 cM, respectively. Twenty-nine previously mapped SSR markers in sorghum were used as anchors, most of the SSR markers in this map ordered collinearly to the published sorghum genetic map, and the distances of common markers intervals similarly. The mapping results also showed that no methylation marker was found on the chromosome SBI-08; methylation markers from both EcoRI/MspI and EcoRI/HpaII enzyme digestions were detected on SBI-02-a and SBI-05; methylation markers from only EcoRI/HpaII enzyme digestion were detected on SBI-02-b; and methylation markers from only EcoRI/MspI enzyme digestion were detected on the other seven chromosomes. High-density methylation regions were revealed near Xtxp 296 on SBI-02-a, Xtxp 69 on SBI-03, and Xtxp 160 on SBI-07. Importantly, MSAP method was first used in the construction of a genetic linkage map. MSAP can be used efficiently to detect DNA methylation polymorphisms, and it is also an efficient technique in constructing genetic linkage map. Furthermore, by finding the methylation sites linking with elite genes, cloning target genes may be facilitated. It is also possible to further study epigenetic phenomena of organisms and explain the mechanism of target gene silencing in genetic transformation by analyzing the regions of high-density methylation sites.