Chromosome location of peroxidase-1

The inheritance of isozyme locus peroxidase-1 (Px1, also called Prx1) was first reported by Hamill (MNL 42:36, 1968). Electrophoretic assays of F2 progeny of crosses between various inbred lines failed to reveal linkage of Px1 with any of the following isozyme loci: Pgd1, Idh2, Goti, Mdh2, Acp1, E1 (Est1), E4 (Est4 and Glu1 (A.L. Kahler, J. Hered. 74:239, 1983).

The chromosomal location of Px1 was determined by analyzing F2 progeny of single-cross hybrids made by crossing selected inbred lines with a series of waxy-marked reciprocal translocations whose genotypes with respect to Pxi had been determined previously. Electrophoretic procedures were as given by Kahler (Crop Sci. 23:572, 1983). Contingency chi-square tests for independent segregation and recombination values were calculated using the maximum likelihood LINKAGE-1 program of K.A. Suiter, J.F. Wendel, and J.S. Case (J. Hered. 74:203, 1983).

Two crosses, both involving wx T2-9d (breakpoints 2L.83, 9L.27), gave highly significant chi-square values indicating linkage and suggesting that Px1 is on the distal portion of the long arm of chromosome 2. The data are as follows:

(wx T2-9d Px1 -2iWF9 Px1 -3) selfed:
  Px1-2/2  Px1 -2/3  Px1 -3/3  
+ 5 78 60 n =248
wx 88 17 0 c2 indep. = 171.45

(wx T2-9d Px1 -2/N7A Px1 -3) selfed:
  Px1 -2/2 Px1 -2/3 Px1 -3/3  
+ 3 64 32 n = 180
wx 68 10 3 c2 indep. = 122.36

Px1 was then mapped with respect to v24 (MNL 61:50, 1987) and pgspt*-579B, two seedling markers provided by Dr. M. G. Neuffer and placed by him on chromosome 2L by B-A translocation tests. v24 has not yet been mapped precisely. Neuffer (pers. comm.) reports that pgspt*-579B is not the same mutant as spt1. Although pgspt*-579B and spt1 are both on 2L and have similar phenotypes, they have not been tested for allelism. S. McCormick and A. Barnason (MNL 59:91, 1985) mapped pgspt* -579B 36 map units distal to v4. Our two-point F2 tests of Px1 with these mutants gave the following data:

(B73 Px1 -2/v24 Px1 -3) selfed:

Px1-2/2 Px1 -2/3 Px1 -3/3
+ 31 77 13 n = 162
v 0 12 29 c2 indep. = 59.59
        15.5 ± 3.1% recomb.

(B75 Px1-2/pgspt*-579B Px1-3) selfed:
  Px1-2/2 Px1-2/3 PA-3/3  
+ 30 70 2 n = 143
pgspt 0 5 36 c2 indep. = 110.92
        4.6 ± 1.79% recomb.

These data confirm the location of Px1 on chromosome 2L, but further tests are needed to determine the order of the three loci. We thank Joanne Mathees for assistance in conducting the electrophoretic assays.

R.H. Whalen and A.L. Kahler*
*Now at Garst Seed Co., Slater, Iowa

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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