SLTAB2 is the paramutated SULFUREA locus in tomato

The sulfurea (sulf) allele is a silent epigenetic variant of a tomato gene (Solanum lycopersicum) affecting pigment production. It is homozygous lethal but, in a heterozygote sulf/+, the wild type allele undergoes silencing so that the plants exhibit chlorotic sectors. This transfer of the silenced state between alleles resembles the process of paramutation that is best characterised in maize. To understand the mechanism of paramutation we mapped SULF to the ortholog SLTAB2 of an Arabidopsis gene that, consistent with the pigment deficiency, is involved in the translation of photosystem I. Paramutation of SLTAB2 is linked to an increase in DNA methylation and production of small interfering RNAs at its promoter. Virus-induced gene silencing of SLTAB2 phenocopies sulf consistent with the possibility that siRNAs mediate the paramutation of SULFUREA. Unlike the maize systems the paramutagenicity of sulf is not, however, associated with repeated sequences at the region of siRNA production or DNA methylation.