The premature senescence mutant (pre1) maps to the long arm of chromosome 1 --Multani, DS, Lee, Y, Johal, G Senescence is the last stage of plant development. The biological role of this process is believed to be in the recruitment or salvage of nutrients from the senescing tissues to developing reproductive tissues. In an effort to understand the senescence at the genetic and molecular levels, we are studying the premature senescence-1 (pre1) mutant of maize.

Steve Briggs first observed this mutant in a randomly Mu-tagged population in 1991 at Pioneer Hi-Bred Int., Inc. The senescing phenotype of pre1, which is inherited in a recessive manner, is apparent 2-3 weeks prior to anthesis (Neuffer, Coe and Wessler, eds., Mutants of Maize, pp. 275-276, 1997). A wave of diffuse chlorosis and necrosis begins at the tip and margins of the leaves and then spreads toward the leaf base. Like natural senescence, the pre1 phenotype starts from the lowermost leaves and then spreads to the top of the plant in a progressive fashion (Fig. 1), causing pre1 plants to senesce completely within weeks after anthesis. Although pre1 plants largely stay male sterile, they do shed pollen occasionally, especially under cool dry conditions. Like most maize mutants that affect tissue integrity, pre1 is easily influenced by genetic backgrounds. For instance, pre1 plants can be maintained in homozygous condition in the B73 background, and its phenotype almost disappears if the brachytic-2 mutation is also in the background.

In order to map pre1 to a specific chromosome, a set of B-A translocation stocks (received from Jim Birchler, University of Missouri-Columbia) was used. Plants heterozygous for this mutation (pre1/+) were pollinated with pollen from hyperploid TB-stocks covering 16 different chromosome arms. The premature senescence mutants (12 out of 62 plants) were observed only in the progeny of crosses involving TB-1La, indicating that pre1 is located on the long arm of chromosome 1.

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