Genetic interactions of c2 and whp and their duplicate function

The effects of c2 and whp on anthocyanins in the plant and in the aleurone tissue are found to be consistent with their duplicate-factor control of yellow pigments in the pollen. So are their effects on yellow fluorescence in bz anthers.

In the plant tissues, c2 Whp B R-r Pl plants have extensive anthocyanin distributed in the sheaths, husks, culm and glumes, and occasional weak pigmentation in the anthers (Coe et al., J. Hered. 72:318, 1981), while c2 whp plants, according to several observations, appear to be completely anthocyaninless. Colorless seeds from F2 progenies segregating for C2/c2 whp/whp B/b Pl/pl segregated for plants similar to c2 B Pl (or pl), each shedding yellow pollen, and green plants, some shedding yellow and some shedding white pollen. Tests are in preparation to check the B constitution of green plants with white pollen in these progenies. Plants with white pollen have expressed no anthocyanin in these pedigrees, or in others with R-r and b, either Pl or pl (c2 Whp plants with R-r b pl have so little color in the anthers that they appear green except in unusual physiological circumstances such as protracted cool conditions; c2 Whp R-r b Pl plants, on the other hand, show light color in the anthers under most conditions; consequently some uncertainty exists with regard to low levels of pigmentation in the absence of extensive observations under diverse conditions). It is not yet clear whether whp is recognizable by effects on plant color in the presence of C2, but the effects are probably not great inasmuch as anthocyanin is present in anthers and glumes in C2 whp R-r b pl plants.

In the aleurone tissue Whp is not normally sufficient for anthocyanin development, judging from the fact that c2 Whp kernels are colorless. However, because c2 in kernels have pale color (Coe, MNL 34:91, 1960), it could be supposed either that in enhances an existing low level of synthesis (i.e., that of Whp) or that in is an active factor replacing (i.e., duplicating) c2, in which case in and whp might be allelic. Crosses were made between c2 whp and c2 gl in and self-pollinated. The F2 ears segregated about 1/4 pale (c2 in) kernels, as expected (in retrospect, 3/16 rather than 1/4). Plantings of pale seeds gave 11 + yellow: 39 gl yellow. Plantings of colorless seeds gave 42 + yellow:2 gl yellow:15 + white:6 gl white. Among gl yellow plants from the pale class self-pollinated, segregations of 3 pale:1 colorless were found (c2/c2 in/in +/whp), and progeny tests of gl white plants from the colorless class show that c2 c2 in in whp whp kernels are colorless. These interactions are consistent with the view that in is an enhancer of pigmentation, so that Whp action generates visible pigment in c2 c2 in in kernels--i.e., that C2 and Whp perform a parallel, duplicate function.

The dramatic yellow fluorescence of bz anthers, which is not blocked by recessive constitutions for a1, a2, bz2, c1, c2 or r-g (unpublished observations), is blocked in white-pollen plants. Progenies to examine this were derived in F2 from Bz bz C2 c2 Whp whp hybrids, selecting colorless kernels and plants with white pollen, crossing them by plants from bronze kernels and repeating the cross the next generation. Three progenies were derived in this way that had the pedigree Bz bz c2 c2 whp whp x bz bz C2 c2 whp whp, from which kernels of the bronze class gave only yellow-pollen plants with yellow fluorescent anthers and kernels of the colorless class gave only white-pollen plants without yellow fluorescence.

These observations, taken with the fact that yellow pollen is conferred by either C2 or Whp, support a conclusion that C2 and Whp have duplicate function in a key initial step in the flavonoid pathway that leads to yellow pigments, anthocyanins, and yellow-fluorescent compounds.

E. H. Coe, Jr.


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