Somatische Konversion (Paramutation) am sulfurea Locus von Lycopersicon esculentum Mill.

Abstract

1. Several lines of Lycopersicon esculentum, which are heterozygous for a mutant sulfurea (sulf) allele vary greatly in the percentage of variegated plants among the heterozygotes. This variegation is caused by somatic conversion (paramutation). The different frequency of conversion is due to the presence of different sulf alleles. Within the sulfurea (pura) (sulf (pura) ) and sulfurea (variegata) (sulf (vag) ) groups there are different alleles, which - though indistinguishable in homozygous condition - can be distinguished by their different conversion activity (paramutagenicity) in heterozygotes with sulf (+). 2. The conversion activity (paramutagenicity) of an allele is expressed by the percentage of green-yellow variegated plants among the heterozygotes (e. g. sulf (pura-90%) means: 90 plants out of 100, which are heterozygous for this particular sulf (pura) allele, are variegated, and 10 are entirely green). 3. The conversion activity (paramutagenicity) of a particular sulf allele can be changed by mutations; it can be either increased or decreased. 4. Crosses have been made between sulf homozygotes (Lycopersicon esculentum, variety Lukullus) and different taxa of the subgenus Eulycopersicon (L. esculentum: marker stocks, German tomato varieties, distantly related varieties from South and Central America; L. pimpinellifolium). Within the subgenus Eulycopersicon the frequency of somatic conversion (paramutation) is - within the range of random and modificative fluctuations - determined only by the conversion activity (paramutagenicity) of the special sulf allele present. Effects of the genetic background could not be demonstrated. Conversion-stable (non-paramutable) sulf (+) isoalleles have not been found in this subgenus. 5. The sulf (pura) group consists of alleles with all possible degrees of conversion activity (paramutagenicity) between 0% and 100% for particular years and average conversion values between 3,6% and 92,9% for several years. The sulf (vag) alleles have a lower conversion activity; its maximum is about 12%. No sulf alleles have been found which have entirely lost their conversion activity. 6. After crossing sulf heterozygotes (L. esculentum) with the distantly related species Lycopersicon hirsutum (subgenus Eriopersicon) and Solanum pennellii significant deviations from the expected 3∶1 segregation for sulf have been found in F 1 and F 3; there is a distinct deficit of sulf sulf seedlings. In F 1 species hybrids somatic conversion (paramutation) occurred very seldom (less than 2%). However in F 2 of both crosses some progenies had frequencies of conversion up to 9,3% (L. esc. x L. hirs.) and 8,5% (L. esc. x Sol. pen.). In F 3 some progenies had frequencies which were slightly higher than those in F 2. In F 4 a progeny has had a frequency of conversion of 61,7%. 7. In F 1, F 2, F 3and F 4 of these species hybrids the sulf (+) allele is from L. hirsutum or S. pennellii and the sulf allele is from L. esculentum; i.e. the system sulf (+) - sulf is always the same. Therefore the differences in ...

SLTAB2is the paramutatedSULFUREAlocus in tomato

“…A sulf homozygote is seedling lethal but a viable heterozygous sulf /+ plant has large chlorotic sectors that are due to paramutation of the active allele to a silenced state in early development. This system is like classic maize paramutation because the paramutated state is heritable and paramutagenic ( Hagemann, 1969 ). SULF maps to the pericentromeric heterochromatin of chromosome 2, at approximately 29 cM from the S locus (Solyc02g077390, compound inflorescence) ( Hagemann and Snoad, 1971 ) but the affected gene could not be mapped precisely due to low recombination frequency in this region ( The Tomato Genome Consortium, 2012 ).…”

Molecular basis of heterosis and related breeding strategies reveal its importance in vegetable breeding

“…Epigenetic modifications play an important role in the formation of plant phenotypes by regulating gene transcription and gene expression 63 – 65 . Alleles of known phenotypes have been studied more extensively in the context of DNA methylation than in the context of other epigenetic modifications 63 .…”

“…2A, B ). A silent epigenetic variant caused by differentially methylated regions (DMRs) in the promoter, sulfurea ( sulf/+ ), can result in homozygous lethal tomato plants that exhibit only chlorotic leaf sectors 64 , 65 . This may occur due to the random combination of genetic information from the parents of the F 1 hybrids because their genotypes are more prone to heterozygosity at the DNA methylation level; this is in line with the findings of Shen et al 59 .…”

CHROMOMETHYLTRANSFERASE3/ KRYPTONITE maintain the sulfurea paramutation in Solanum lycopersicum

“…In crosses between variegated sulf lines and their parental WT lines paramutation is poorly penetrant in F1 (<12%) (17). In F2, the percentage of variegation among heterozygous also varies, further showing that sulf has incomplete penetrance (5,17). These differences in paramutation penetrance have been linked with the existence of different sulfurea epi-alleles with different degrees of paramutagenicity (5,17).…”

“…In plants the DNA is methylated at the paramutated (silenced) sequence region, but this modification is not sufficient to mediate paramutation, because many methylated loci do not show paramutation. Early examples of paramutation in maize (1), pea (4) and tomato (5) have striking phenotypes based on pigmentation or gross morphology. However, from genome-wide DNA methylation analyses, there is now evidence that paramutation-like effects may be more widespread (6)(7)(8).…”