Paramutation at the sulfurea locus of Lycopersicon esculentum Mill.

Abstract

1. In tomato plants heterozygous for a mutant allele of the sulfurea (sulf) locus paramutation may take place: under the influence of a paramutant sulf allele, the paramutable wild type allele sulf (+), which is present in the same nucleus, is heritably altered with a definite frequency to a sulf mutant allele, either of the sulf (pura)or the sulf (vag)group. 2. A number of the sulf (+) sulf heterozygotes remain entirely green during their whole ontogenetic development (type I plants, without paramutation). However, others of the plants become variegated: these variegated plants contain-apart from green sectors - only yellow-green speckled sulf (vag)sectors (type II plants), or only pure yellow sulf (pura)sectors (type III plants) or both sulf (vag)and sulf (pura)sectors side by side (type IV plants). 3. For all variegated plants (types II, III and IV) we determined the sizes of the green and of the paramutant sulf (vag)and sulf (pura)sectors and made a statistical analysis of the values obtained. 4. We conducted observations over a period of three years and obtained following findings: type II plants (with sulf (vag)sectors) have an average size of the paramutant sectors of 27.9% (the whole plant being 100%). Type III plants (with sulf (pura)sectors) have an average sector's size of 25.7%, whereas the size of the paramutant sectors in type IV plants (with both sulf (vag)and sulf (pura)sectors) amounts to 54.4% (35.7% sulf (vag)and 18.7% sulf (pura)). Thus, the occurrence of tissues of both phenotypes in one plant has, on the average, been found to be correlated with a doubling of the proportion of paramutant sectors in that plant. 5. Within sulf (+) sulf heterozygotes there is, in general, a positive correlation between the frequency of paramutant plants and the proportion of paramutant sectors within the plants. This is mainly due to the fact that there is a significant positive correlation between the frequency of type IV plants and the frequency of paramutant plants, i.e. the more plants within a progeny variegated, the greater the frequency of type IV plants containing both sulf (vag)and sulf (pura)sectors. 6. These findings (mathematically analysed and compared with the consequences of several models) may result in the following concept: the paramutation processes in sulf (+) sulf heterozygotes are restricted to a small group of cells (16 cells at the most) during a short period of about three cell generations after seed germination and expansion of the cotyledons. In the course of which, the probability for the occurrence of paramutation decreases rather quickly from one cell generation to the next. These characteristics of paramutation processes mentioned cause the occurrence of rather large and well defined sectors of paramutant tissue.

Will epigenetics be a key player in crop breeding?

“…The non-Mendelian pattern of inheritance typical of paramutation was first observed in studies of the genetics of "rouges" in cultivated peas (Pisum sativum L.; Bateson and Pellew, 1915). and subsequently in studies of the inheritance of pigmentation phenotypes associated with the anthocyanin pathways in maize (Brink, 1956), and in studies of inheritance at the sulfurea locus in tomato (Hagemann, 1958;Hagemann and Berg, 1978). The power of the anthocyanin pigment pathway as a model for genetic studies in maize, perhaps combined with the importance of maize as a major food crop, has led to advances in understanding the biology and molecular genetics of paramutation in this species (Hollick, 2017;Springer and Schmitz, 2017).…”

Anthocyanins in Staple Crops

“…Also, dosage effects caused by ploidy changes seem to influence the paramutation as has been demonstrated in the tomato sulf locus [86] and in Arabidopsis active hygromycin phosphotransferase ( HPT) transgene locus [82].…”

Paramutation: Heritable in TransEffects

“…The epigenetic state of some paramutable and paramutagenic alleles is very stable (paramutable P-rr and sulf alleles; paramutagenic A1, b1, HPT, p1, r1 alleles; Hagemann, 1993;Das and Messing, 1994;Brink and Weyers, 1957;Coe, 1959;Sidorenko and Peterson, 2001;Mittelsten Scheid et al, 2003). Some paramutable and paramutagenic alleles can however spontaneously change into the other epigenetic state (paramutable 'ear rogue', b1, A1, Ph-Rh, and Spr12F spt alleles and paramutagenic Pl' allele; Bateson and Pellew, 1915;Coe, 1959;Meyer et al, 1993;Hollick et al, 1995;English and Jones, 1998).…”

“…Some paramutable and paramutagenic alleles can however spontaneously change into the other epigenetic state (paramutable 'ear rogue', b1, A1, Ph-Rh, and Spr12F spt alleles and paramutagenic Pl' allele; Bateson and Pellew, 1915;Coe, 1959;Meyer et al, 1993;Hollick et al, 1995;English and Jones, 1998). Furthermore, a number of alleles also display a series of intermediate epigenetic states, rather than one paramutable and one paramutagenic state (sulf, A1, pl1, and p1; Hagemann and Berg, 1978;Hagemann, 1993;Meyer et al, 1993;Hollick et al, 1995;Sidorenko and Peterson, 2001).…”