The controlling elements Fcu and arv-m594 map to chromosome 2

--Stinard, PS

Fcu was first identified by Gonella and Peterson (Genetics 85:629–645, 1977) as the factor responsible for aleurone color sectoring at the r1 locus in Cuna tribal maize from Colombia. The Fcu system was found to be comprised of two elements: a responsive r1 haplotype, r1-cu, and the controlling element Fcu. r1-cu produces a variable pale aleurone coloration in the absence of Fcu, but produces sectors of full color pigmentation on a pale background in the presence of Fcu. Two other r1 haplotypes, R1-r(sd2) (spotted dilute2; also referred to as R-r#2; Gonella and Peterson, Molec Gen Genet. 167:29–36, 1978) and R1-mo(cu) (Gonella and Peterson, MNL 50:61–63, 1976) were subsequently found to produce sectoring in the presence of Fcu as well.

In MNL 77:77-79, we reported that the haplotypes R1-ch(Stadler), R1-d(Catspaw), R1-Randolph, R1-r(Venezuela 412-PI302347), and R1-r(Venezuela559-PI302355) also respond to Fcu. It is not clear whether the response at the r1 locus is a direct one, or whether Fcu elicits its phenotype through interaction with intermediaries such as enhancers or suppressors of r1 aleurone color expression.

Other genetic factors called arv-m’s (mutable amplifiers of aleurone color in certain R1-Venezuela haplotypes; Kermicle, MNL 77:52, 2003) also elicit aleurone color sectoring in crosses to the same haplotypes and may be similar, if not identical, to Fcu. As a first attempt at characterizing the similarities and differences between these controlling elements, Fcu (isolate PAP74-1033-8 received from Peter Peterson of Iowa State University) and arv-m594 (an arv-m element isolated from one of Brink’s R1-r(Venezuela594-PI302363) lines, Stock Center ID# X235B) were mapped using a series of wx1 marked A-A translocations. Mapping crosses involving the translocations T1-9c, T1-9(4995), T1-9(8389), T3-9(8447), T3-9(8562), T4-9e, T4-9(5657), T5-9c, T5-9a, T6-9b, T7-9(4363), T7-9a, T8-9d, T9-10b, and T9-10(8630) failed to show linkage between wx1 and Fcu (data not shown). Mapping crosses involving the translocations T1-9c, T1-9(5622), T1-9(8389), T3-9(8447), T3-9(8562), T4-9e, T4-9(5657), T5-9(022-11), T5-9a, T6-9e, T7-9(4363), T7-9a, T8-9d, T9-10(059-10), and T9-10b failed to show linkage between wx1 and arv-m594. However, mapping crosses involving T2-9c, T2-9b, and T2-9d showed linkage of wx1 with both Fcu (Table 1) and arv-m594 (Table 2).

Both Fcu and arv-m594 show the same general patterns of linkage with wx1 in the T2-9 translocations (Tables 1 and 2). It should be noted that the T2-9c data show distortions in the ratios of waxy to nonwaxy kernels indicative of the transmission of duplicate-deficient chromosomal segments through the female. The linkage was tightest with T2-9d (2L.83; 9L.27; 13.6 and 9.4 centiMorgans, respectively) and weakest with T2-9c (2S.49; 9S.33; 39.3 and 30.8 cM, respectively), indicating that both factors probably reside on the long arm of chromosome 2. However, the linkage values are clearly not identical for the two factors, all linkage values lying well outside each other’s standard errors in side by side comparisons. These differences could be due to differences in chromosomal location for the two factors, but they could also be due to differences in genetic background between the lines, which are known to affect linkage values. No conclusions as to whether Fcu and arv-m594 map to the exact same chromosomal location can be drawn based on these data. In order to resolve this question, direct mapping crosses will be made between Fcu and arv-m594, as well as mapping crosses of Fcu and arv-m594 with the chromosome 2 marker stock fl1 v4 w3 Ch1.

Testcross: [Wx1 T fcu r1 × wx1 N Fcu r1] × wx1-m8 N fcu R1-r(sd2)

¹Total of 4 crosses.
²Total of 7 crosses.
³Total of 5 crosses.

Testcross: [wx1 T arv r1 × Wx1 N arv-m594 R1-r(Venexuela594-PI302363)] × wx1-m8 N arv R1-r(sd2)

1Total of 6 crosses.
²Total of 4 crosses.
³Total of 4 crosses.