Iowa State University
Northeast Missouri State University
vp2-5080, a new mutable allele of vp2 with large revertant sectors
--Philip S. Stinard and Brent Buckner
A recessive pale yellow endosperm mutant with yellow revertant endosperm sectors was found segregating on the selfed ear of a plant (84-5080-13) grown from the outcross to standard of a putative Mutator-induced wx mutant, wx-Mus2j. When planted in the sandbench, pale yellow mutable kernels gave rise to albino seedlings with a heavy mutability pattern of large (many cells in width) and small (one to a few cells in width) longitudinal green sectors. This mutant was given the designation wmut*-5080.
Allele tests of wmut*-5080 to known white endosperm/albino seedling mutants, including al, cl, lw1, lw2, vp2, vp5, vp9, w3, y9, and y10, proved negative. Crosses of wmut*-5080 heterozygotes by a set of B-A translocations involving 19 of the 20 maize chromosome arms failed to uncover the mutant phenotype. The simpler methods of locating the mutant to chromosome having failed, wmut*-5080 heterozygotes were crossed to a series of wx marked translocations with breakpoints near the centromeres of the non-9 chromosomes. The F1's were selfed and outcrossed to standard wx testers. Only selfed ears of the F1 between wmut*-5080 and wx T5-9(4817) (5L.06, 9S.07) showed evidence of linkage (repulsion) between wmut*-5080 and wx. The outcross to wx of one of these ears was grown in Don Robertson, D's 1990-91 winter nursery, the resulting plants self pollinated, and the selfed ears scored for semisterility, wx, and wmut*-5080. The results of this linkage test are reported in Table 1, and indicate tight linkage between wmut*-5080 and T5-9(4817) (p=1.8±0.8cM).
Table 1. Three-point linkage data for wx T5-9(4817) vp2-5080.
Testcross: (wx T5-9(4817) Vp2 / Wx n vp2-5080)
X wx wx n n Vp2 Vp2
|0||wx T +||126|
|+ n vp||135||261|
|1||wx n vp||2|
|+ T +||3||5|
|2||wx T vp||2|
|+ n +||2||4|
|1+2||wx n +||1|
|+ T vp||0||1|
Elsewhere in the 1990-91 winter nursery, wmut*-5080 was allele tested with the chromosome 5 mutants vp2 (a repeat of an earlier allele test, this time using the Maize Stock Center's vp2 stock) and ps. This time, the allele test with vp2 proved positive. (A check of the pedigree of the vp2 stock we had used for the earlier negative allele test revealed ambiguities that rendered its genetic identity suspect.) We have given wmut*-5080 the designation vp2-5080.
During the course of propagating and mapping vp2-5080, we found that expression of this mutant varied widely from mutable to stable, from viviparous to dormant, from pale yellow to nearly white endosperm, and from albino seedling to pastel seedling. We have not crossed vp2-5080 into isogenic lines to determine the cause of these variations. However, variation in dormancy and seedling phenotype has been observed in certain alleles of vp9 and w3 (Robertson, DS, J. Hered. 66:67-74, 1975), and may be due to segregating genetic modifiers. Similar, or perhaps identical modifiers may be at work in vp2-5080.
The only other known mutable allele of vp2, vp2-grmos
(Robertson, ibid.), produces large revertant sectors in both endosperm
and seedling. We note the similarity in mutability pattern between vp2-5080
and vp2-grmos, but it remains an open question as to whether this
pattern of mutability is inherent to mutable alleles of vp2.
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