Comparative mapping of Andropogoneae: Saccharum L. (sugarcane) and its relation to sorghum and maize

Abstract

Comparative genetic maps of Papuan Saccharum officinarum L. (2n = 80) and S. robustum (2n = 80) were constructed by using single-dose DNA markers (SDMs). SDM-framework maps of S. officinarum and S. robustum were compared with genetic maps of sorghum and maize by way of anchor restriction fragment length polymorphism probes. The resulting comparisons showed striking colinearity between the sorghum and Saccharum genomes. There were no differences in marker order between S. officinarum and sorghum. Furthermore, there were no alterations in SDM order between S. officinarum and S. robustum. The S. officinarum and S. robustum maps also were compared with the map of the polysomic octoploid S. spontaneum 'SES 208' (2n = 64, x = 8), thus permitting relations to homology groups ("chromosomes") of S. spontaneum to be studied. Investigation of transmission genetics in S. officinarum and S. robustum confirmed preliminary results that showed incomplete polysomy in these species. Because of incomplete polysomy, multiple-dose markers could not be mapped for lack of a genetic model for their segregation. To coalesce S. officinarum and S. robustum linkage groups into homology groups (composed of homologous pairing partners), they were compared with sorghum (2n = 20), which functioned as a synthetic diploid. Groupings suggested by comparative mapping were found to be highly concordant with groupings based on highly polymorphic restriction fragment length polymorphism probes detecting multiple SDMs. The resulting comparative maps serve as bridges to allow information from one Andropogoneae to be used by another, for breeding, ecology, evolution, and molecular biology.

Figure 1

Comparative genetic maps of maize, sorghum, and three species of Saccharum. DNA marker positions in maize were based on the UMC maize RFLP map (http://teosinte.agron.missouri.edu). Sorghum linkage groups (LGs) were named according to Chittendenn et al. (44). Sorghum marker positions were compiled based on Whitkus et al. (12), Pereira et al. (43), Lin et al. (20), and Paterson et al. (21); their map locations are indicated by an arrow. S. spontaneum ‘SES 208’ homeology groups (HGs) were based on daSilva et al. (5). DNA markers whose positions conflict with the sorghum comparisons have their location indicated in parenthesis, using “S” for sorghum and “M” for maize. Linkage groups were formed by using RFLP, AFLP, and arbitrarily primed PCR markers, but those shown are only the RFLP markers because they enabled the comparisons. Probes that have been mapped in a species have their position indicated with a line that traverses the chromosome or linkage group, whereas probes whose positions are unknown (i.e., not mapped) contain lines that pass behind the chromosome or linkage group. Maize probes unmapped in sorghum have arrows indicating their inferred position in sorghum (based on combining information from previous maps). Breaks in the LGs or chromosomes indicate discontinuity of the LGs or chromosomes. For maize chromosomes, S = short arm and L = long arm. (Bar = 10 cM.)