The monogenic root mutant rtcs is completely deficient in the formation of all nodal roots (lateral seminal-, crown- and brace roots). The defect of the mutant is effective very early in root initiation since no primordia formation for the affected root types can be detected microscopically in relevant tissue slices. This loss of function feature of rtcs is of particular interest, and work towards the isolation of the affected gene is underway. The mutant locus had previously been mapped to the short arm of chromosome 1 with the help of a cosegregating RAPD marker (Hetz, W. et al., Plant J. 10:845-847, 1996). We have now performed a more extended mapping analysis by working with microsatellites specific for chromosome 1, which have been found to be polymorphic for rtcs plants in the F2 mapping population of A632 x rtcs. The outcome of this work is summarized in the map segment of chromosome 1 shown in the Figure. It can be seen from the marker positions that rtcs is located 10 cM from bmc1014 and 3 cM from bmc1083 while bmc1627 has shown no recombination with rtcs (130 plants tested). This result is now used as a basis for a fine mapping of rtcs with the AFLP procedure.
 

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