Somatic reversion of a Xantha-like gene in soybean by fast neutrons and X rays

The variety T219 of Glycine max (soybean) has a wild-type chlorophyll development gene Y11 and its allele y 11. Seeds from autogamous T219 plants produce dark green (Y11Y11), light green (Y 11y11) and yellow (y11 y11) seedlings. Upon irradiation of dry seeds with X rays, the frequency of light-green mosaics on y11 y11 simple leaves was about twice as high as that of dark-green mosaics on Y11y11 simple leaves. For the explanation of the two-fold difference in mutability, we propose that both the light-green and the dark-green mosaics are caused by reversion of y11 to Y11, as the number of target gene y11 per cell in the y 11y11 tissue is twice that in the Y 11y11 tissue. Somatic reversion of the y11 gene was induced, in either y11 y11 or Y11y11 plants by 14 MeV neutrons and by fission neutrons at a rate about 20 times higher than that by X rays, suggesting that the reversions result from deletion mutations. To explain the occurrence of the reversion by deletions, we assume that the y11 gene is a complex gene made of a transposable element inserted at the Y 11 locus and that the reversion resulted from the deletion of the inserted transposon. The phenotype of the y11 gene shares many similarities with those of Xantha genes mapped at several loci in barley and tomato.