Spf from the Spotted-dilute system is a member of the En/Spm controlling element family

--Stinard, PS

The Spotted-dilute controlling element system was originally characterized as a three element system involving the autonomous element Spf (spotting factor), a receptor at the r1 locus in the haplotype R1-r(sd2) (spotted dilute2), and a third factor called Dil (diluting factor) that suppresses background aleurone coloration in crosses involving R1-r(sd2) (Sastry and Kurmi, MNL 44:101–105, 1970). Another haplotype that responds to Spf, R1-r(sd4) has apparently been lost. There are several reported peculiarities of this system that set it apart from other controlling element systems, and these peculiarities will be addressed in a separate report in this MNL. Sastry and Kurmi tested Spf against the Ac Ds system and found no interaction. However, preliminary data showed that lines carrying Spf induced mutability at a2-m1::dSpm. Fincham and Sastry (Annu Rev Genet 8:15-50, 1974) cite control of R1-r(sd2) by Spm. In contrast, Singh, Sachan, Guha, and Sarkar (MNL 49:45–49, 1975) obtained negative results when they tested Spf against c2-m2::dSpm. In order to resolve these inconsistencies and simplify analysis of the Spotted-dilute system, several tests were conducted to explore the relationship between the Spotted-dilute and En/Spm systems.

In pilot projects to find appropriate combinations of autonomous elements and receptors for both systems, crosses of Spf were made to dSpm/I testers, and crosses of En/Spm were made to R1-r(sd2). For crosses of Spf to a1-m1-5719::dSpm sh2, 14 plants were obtained that showed mutability at both R1-r(sd2) and a1-m1-5719::dSpm, and 5 were obtained that showed mutability at neither. There were no instances of mutability at one locus, but not the other. For crosses of Spf to wx1-m8::Spm-I8, 4 plants were obtained that showed mutability at both R1-r(sd2) and wx1-m8::Spm-I8, and 6 that showed mutability at neither. Again, there were no instances of mutability at one locus but not the other.

For crosses of a1 Spm-S Sh2 wx1-m8::Spm-I8 to R1-r(sd2), 8 out of 9 plants showed mutability at both wx1-m8::Spm-I8 and R1-r(sd2). 1 plant showed mutability at R1-r(sd2) but not at wx1-m8::Spm-I8. The possibility that the latter event represents an excision resulting in a stable null derivative of wx1-m8::Spm-I8 has not been ruled out. Finally, for crosses of o2-m12::Spm to R1-r(sd2), 8 out of 8 plants showed mutability at both loci.

These results are highly suggestive of Spf and R1-r(sd2) being members of the En/Spm controlling element system. To demonstrate this more conclusively, followup crosses were made involving Spm, wx1-m8::Spm-I8, and R1-r(sd2) for the ease of scoring mutability at wx1 and r1 simultaneously on individual kernels. The cross was set up as follows: [R1-r(sd2) Wx1 A1 Sh2 × R1-r(sd2) wx1-m8::Spm-I8 a1 Spm-S Sh2] × R1-r(sd2) wx1-m8::Spm-I8 A1 Sh2 Dil. Two ears resulting from this cross segregated 1:1 for mutable and stable aleurone color indicating segregation for one Spf element, and approximately 1:1 for starchy and waxy due to heterozygosity at the wx1 locus (there was a shortage of waxy kernels in one cross resulting in a deviation from 1:1 significant at the 5%, but not the 1% level). The waxy kernel class was scored for mutability at the wx1 locus indicative of the presence of En/Spm. Complete kernel counts are given in Table 1. Of the kernels scorable for both wx1 and r1 mutability, 223 showed mutability at both loci and 226 showed mutability at neither (with no exceptions), demonstrating a complete correlation between the presence of En/Spm and Spf in a population of 449 individuals. Additional tests will be conducted in order to boost these numbers, but it is safe to conclude that En/Spm and Spf are functionally equivalent.

1:1:1:1 χ² = 4.679 (p<0.05)
1:1 χ² for Wx to wx = 4.652 (p<0.05)
1:1 χ² for cl mutable to cl stable = 0.026 (NS)