Current status of the Tripsacum dacyloides (Eastern gamagrass)
RFLP molecular genetic map
--C.A. Blakey, E.H. Coe, Jr. and C.L. Dewald
Tripsacum genetic map. The restriction fragment length polymorphism (RFLP) genetic map developed from the segregation of molecular markers in a diploid (2n=36) F2 population of Tripsacum dactyloides (common name: Eastern gamagrass) currently stands at 16 linkage groups markers (see Figure) (Blakey, Ph.D Dissertation, 1993; Blakey et al., manuscript in preparation). The map includes 61 loci identified by 57 molecular markers and one phenotypic marker (gsf1) (Blakey et al., submitted), for a total genetic length of 609 cM (Group A = longest at 210 cM, Group P = shortest at 4 cM). Complete map data will be available in the Maize Database, upon publication of the RFLP map.
A total of 358 molecular probes have been screened, including 20 functionally defined maize probes, and 197 detected polymorphisms in T. dactyloides with one or more enzymes. The polymorphic markers included 65 T. dactyloides genomic DNA probes (TDA), 117 maize genomic DNA probes (BNL, NPI, PHP, UMC), 13 functionally defined maize probes, one functionally defined barley probe, and one wheat genomic DNA probe. Over 50 TDA markers and 60 maize RFLP markers that exhibited polymorphism between the T. dactyloides parental lines remain to be placed on the existing Tripsacum map.
Maize map: All 112 TDA genomic DNA markers screened against the T. dactyloides parental lines have also been screened for polymorphisms in the maize lines Tx303 and CO159. Seven TDA markers representing 8 loci in maize (ztda loci, for Zea mays ssp. mays loci identified by TDA genomic DNA probes--see Blakey et al., next article) have been placed on the UMC maize map (MNL 67 and MNL 68). Additional mapping is in progress.
Analysis of Zea/Tripsacum genome synteny: Analysis of genomic synteny between Tripsacum and maize has revealed regions/blocks of markers that appear to be conserved between these two species from different genera (Blakey, Ph.D Dissertation, 1993; Blakey et al., manuscript in preparation). Every RFLP linkage group of these two species exhibits some degree of synteny, from having a single molecular marker in common to four-marker blocks of conserved order. And, in 9 out of 14 cases, the conserved linkage blocks indicate approximately the same genetic distance (within 10 cM) over the conserved region.
Relevant to linkage group conservation, most of the T. dactyloides linkage groups have markers in common with two maize linkage groups. Five T. dactyloides groups have markers in common with only one maize group, nine T. dactyloides groups have markers in common with two maize groups, and twoT. dactyloides groups (D and N) each have markers in common with three different maize linkage groups. In general, the particular maize linkage groups in common with a T. dactyloides group differ from those maize groups found in common with individual sorghum linkage groups seen by Whitkus et al. (Genetics 132:1119-1130, 1992) and Binelli et al. (TAG 84:10-16, 1992). The exception was Tripsacum group E and Whitkus's sorghum group H, both of which have markers from maize groups 4 and 5, and have overlapping or conserved regions in common.
Summary: Through the use of molecular probes derived from both maize and Tripsacum dactyloides, a genetic map using molecular markers has been constructed in T. dactyloides resulting in 16 linkage groups. The mapped maize-derived markers included loci from all ten maize chromosomes scattered on 16 Tripsacum linkage groups with large numbers of loci clustered in fourteen syntenic regions conserved between the two genomes on 12 different Tripsacum linkage groups and 8 different maize chromosomes. In general, the recombination distances of these regions in maize were greater than or equal to homoeologous regions in Tripsacum, with the exception of tumc83 - tumc161(Tripsacum group A; homoeologous region on maize chromosome 1) covering a distance of 132 cM in Tripsacum and only 55 cM in maize. In comparing the Tripsacum linkage groups to the maize molecular and genetic maps, a few of the homoeologous Tripsacum chromosomes described by Galinat (1974) were tentatively identified, Tr5, Tr7, and Tr9 (see Table), correlating the cytogenetic, genetic and molecular maps for these chromosomes.
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