A mutable kernel type showing purple or red spots on a colorless background was found by Dr. G. F. Sprague at the University of Illinois. This kernel type arose from corn lines with aberrant ratios for the A gene (Sprague and McKinney, 1971). Control of this spotting is associated with the A1 locus.

Relationship of the mutability to other controlling element systems: In order to test the relationship between this mutable kernel type and presently known controlling element systems experiments were conducted with the receptor alleles of the En, Ac, Dt and Fcu systems. The general nature of this cross with the new mutable a1 allele (a1-m*):

Diagram.

This type of test confirms that the En receptor allele, a2-m(r), is not triggered to show spots and further confirms that the a1-m* allele was present. Thus, the mutability of the a1-m* allele does not contain an En element. Similar procedures conducted with the receptor alleles of the regulatory elements Dt, Ac, and Fcu indicated that the component triggering mutability for a1-m* is not one of these regulatory elements:

A two-unit system is uncovered: In a number of crosses of this mutable kernel type by an a1 tester (a1-m* Sh2/a1-m* Sh2 x a1 sh2/a1 sh2, all other color genes dominant; the a1 allele linked to sh2 is a non-mutating allele) completely colorless kernels arose. Repeated selection and testing of mutable kernel progeny (a1-m* Sh2/a1 sh2 x a1 sh2/a1 sh2) yielded colorless kernels among the round progeny. When these colorless kernels were tested with the sib colorless shrunken sibs from the same ear, mutability resulted. The segregation of mutable and colorless kernels among the round progeny (1/2:1/2) leads to the conclusion that a separable factor has been uncovered that triggers the mutability of a colorless allele. Because of its non-relationship to the other systems, this finding establishes a new system of mutability to be added to the previously described systems.

This system is designated with a regulatory element, Ub, (Ubiquitous--basis described below) and a receptor element, Rub, for receptor of Ub signals. The colorless a1 allele responding to Ub is a1-Rub. Thus,

Ub + a1-Rub = mutable--purple or red spots on colorless background

a1-Rub = colorless

Ub + a1 sh2 = colorless--an a1 allele that does not respond to any regulatory element.

The prevalence of Ub: In outcrosses of a1-Rub plants (without Ub) to unrelated a1 tester lines (unrelated in having no history of crosses with plants containing Ub), an unexpected result was observed. In every case in crosses with these unrelated a1 tester lines, mutability was found, indicating that Ub is present in these unrelated lines. The pervasiveness of this regulatory element prompted the naming of this new system Ubiquitous (Ub).

Crosses to assorted lines are now being tested to explore the prevalence of Ub in many unrelated inbred lines. It should be noted that the presence of Ub would escape detection without the availability of the a1-Rub tester.

Peter F. Friedemann and Peter A. Peterson

Return to the MNL 54 On-Line Index
Return to the Maize Newsletter Index
Return to the MaizeGDB Homepage