Plant Gene Expression Center, USDA-ARS

Location of Adh1 and Kn1 on the linkage map

--Julie Mathern and Sarah Hake

We undertook a RFLP mapping study of the long arm of chromosome 1 in order to place Kn1 and Adh1 on the map and to orient them with respect to the centromere. One of the purposes of this study was to characterize the endpoints of a deletion of Kn1.

The material used for segregation analysis was from self-pollinations of Kn1-N1 Adh1-S Lw/kn Adh1-Fgamma25 lw heterozygotes. Seedlings were green and knotted, or white and normal, unless there was recombination. Southern blots of DNA from these individuals were probed with a Kn1 probe (Hake, Vollbrecht, Freeling in press), an Adh1 probe and the RFLP markers shown in the table. We were able to place Kn1 and Adh1 on the RFLP map between UMC107 and BNL7.25. We found 2 recombinants, one green and normal and the other white and knotted, at the frequency of 1/200. The proximal marker, UMC 107, segregated with Kn1 and the distal markers segregated with Adh1 (and lw), demonstrating that Kn1 is proximal to Adh1. In both cases the Adh1 allele cosegregated with its linked lw marker, thus we have not yet determined the placement of Adh1 relative to lw.
UMC 37 17 35
BNL8.10 22 23 proximal
UMC 107 65 6.9 
BNL 7.25 38 8 distal
BNL 8.29 17 26

We recovered a deletion of Kn1 following X-ray mutagenesis that is not transmissible through the male. The deletion does not include Adh1 or lw (Hake, Vollbrecht, Freeling, in press). Since we have placed Adh1 and lw distal to Kn1, we know this deletion extends less than 1 map unit in the distal direction. Recombination to a proximal marker, Bz2, does not appear to be affected by the deletion. 68 recombinants were found out of 284, giving a distance of 24mu, similar to the distance on the genetic map of 22mu. Therefore, the deletion is relatively small. We tried to uncover the deletion by crossing it to the TB-1La translocation using Adh1 markers to distinguish the progeny. We could not recover the genotype for the hypoploid/deletion double heterozygote in healthy kernels. The ear however did contain defective kernels. This suggests that the deletion is also homozygous lethal to the embryo. We are curious whether it is the absence of Kn1 or a closely linked gene that makes it lethal.

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