A correlation between endosperm and seedling phenotypic variation in an allelic series of et1 mutants

--M. S. Scanlon, P. S. Stinard, M. G. James and D. S. Robertson

An earlier report (MNL 64:11) described allelic variation in the endosperm phenotypes of our putative mutator-tagged alleles of the et1 locus. Currently our study has identified 11 independently induced et1 alleles (see mapping article by James et al., this issue), which display great variation in the degree of etching and/or shrinkage of the endosperm. In addition to the endosperm phenotype, the et1 allele is pleiotropic and confers a virescent seedling phenotype. In order to investigate the variation in the seedling virescence of these alleles, representative Mutator-tagged et1 endosperm variants were sandbench tested. The results are given in Table 1; the non-Mutator induced standard et1 allele was included for the sake of comparison.

Table 1. Kernel and seedling phenotypes of putative Mu-induced et1 alleles.
 
Mutant designation Kernel phenotype Degree of etching Seedling phenotype
et standard "normal" etched moderate virescent
et1-Mu*3328 (a) severely etched extreme virescence extreme, albino
et1-Mu*2320 (a) severely etched extreme virescence extreme, albino
et1-Mu*24 (a) mild shrunken none to slight mostly green, pale stripes
et1-Mu*2457 (a) severely shrunken moderate virescent
et1-Mu*2320 (b) small, sugary, defective kernel is shriveled lethal
et1-Mu*2162 (b) small, sugary, defective kernel is shriveled lethal

(a) data from heterozygotes with standard etched (et1/et1-Mu)

(b) data from homozygous mutant kernels (et1-Mu/et1-Mu)

These results indicate that the severity of the virescent phenotype may be correlated with the degree of etching and not the shrunkenness of the endosperm. Despite the extreme albino phenotype of the et1-Mu*3328 and et1-Mu*2320 seedlings grown from severely etched seed, these seedlings do eventually become green, and thus are truly virescent. Cox (MNL 42:52-56) reported similar results from seedlings grown from severely etched kernels. The lethality of the et1-Mu*2320 and et1-Mu*2162 sugary defective kernels is attributed to the absence of a germ. The small defective kernel phenotype is seen on self-pollinated ears of these two alleles only. It should be noted that variation in seedling and endosperm phenotypes is exhibited within, as well as between, et1-Mu allelic families. Possible causes of the phenotypic variations described herein include: variable expression of et1 due to different Mutator element insertion sites or Mu-induced deletions; genetic background effects, although each of the alleles described has been outcrossed to standard Q60 and standard B70 backgrounds for at least three generations; the presence of a modifier of etched (Met) as described by Cox in MNL 40:39-42.


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