--Yong-Bao Pan and Peter A. Peterson

In the progeny test of the dominant mutant Mn-866248U (MNL 61:6), another example of Uq element activity (independent of the Uq element at the mn locus) was found. Upon selfing, half of the progeny ears, arising from either the miniature spotted or the colorless normal sib kernels of the ear 866248U/5121-7, segregated for smaller seeds with very small, near single-cell spots (10aa, Reddy and Peterson, MGG 194:124, 1984) at about .25 frequency (data not shown). An example of this type ear is shown in the Figure with top and side views of a 10aa spotted smaller seed.

Since both parents of the cross (866248U x 5121-7) had the a-ruq reporter allele (a-ruq/a-ruq) genotype and were normal, this 10aa spotted smaller-seed phenotype must be due to an interaction of the a-ruq reporter allele with two homozygous activated Uq elements. On the other hand, since the selfed ear of plant 865121-7 produced only 333 colorless normal kernels, the activation event must have occurred in the maternal plant 866248U that had been treated with 5-aza-2-deoxycytidine. This Uq element is tentatively designated as Uq-10aa-SS (Smaller Seed).

Figure. Phenotype of a-ruq/a-ruq Uq-10aa-SS/Uq-10aa-SS.

Our effort in studying the genetics of the element was hampered by the fact that when the 10aa spotted smaller seeds were planted none of the 72 established a plant either in the greenhouse or in the field. This brings up a very interesting question of whether this element affects the fitness of the genotype a-ruq/a-ruq Uq-10aa-SS/Uq-10aa-SS.

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