The Sn locus conditions anthocyanin accumulation in specific plant and seed tissues. The Sn accessions we have been studying map on the long arm of chromosome 10 about 2 cM R distal and they differ in their rate of accumulation and in the quantity of pigment. Since they were originally present in different populations, they will be referred to as geographic alleles. Their origin and phenotypes are reported in Table 1. Their characterization at the molecular level could provide information useful in understanding the basis of the observed differences in expression. As reported in this MNL, Sn:bol3 crosshybridizes to a fragment (pR-nj: 1) cloned from R-nj. Genomic DNA from plants homozygous for r Sn:bol1, r Sn:bol2, r Sn:bol3, r Sn:Coop, R Sn:Stadler and r Sn:Hopi were digested with SstI and analyzed by Southern blot. The pR-nj: 1 probe detects SstI fragments of different size in all genotypes tested. The Sn:bol1 hybridization pattern is the same as that of Sn:bol3, thus showing a complex gene structure, while the Sn:bol2 pattern appears less complex. The other three alleles show a high structural polymorphism indicating that they differ both from Sn:Bol3 as well as from each other. These preliminary results indicate that the Sn alleles tested are related in terms of DNA homology because they all cross-hybridize but appear unrelated in terms of structural DNA polymorphism thus proving to be distinct alleles.
Table 1. Description of the Sn accessions analyzed. The signs + and - indicate presence and absence of pigmentation while (+) refers to weak pigmentation (sct:scutellum; al:aleurone; sn:scutellar node; msc:mesocotyl; plant:leaf basis and midrib, pericarp).
C. Tonelli, G. Consonni, S. Dellaporta1 and G. Gavazzi
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