Three non-allelic epistatically interacting methyltransferase mutations produce novel tocopherol (vitamin E) profiles in sunflower.

Wildtype sunflower ( Helianthus annuus L.) seeds are a rich source of α-tocopherol (vitamin E). The g = Tph ₂ mutation disrupts the synthesis of α-tocopherol, enhances the synthesis of γ-tocopherol, and was predicted to knock out a γ-tocopherol methyltransferase (γ-TMT) necessary for the synthesis of α-tocopherol in sunflower seeds—wildtype ( g ⁺ g ⁺) lines accumulated > 90% α-tocopherol, whereas mutant ( g g) lines accumulated > 90% γ-tocopherol. We identified and isolated two γ- TMT paralogs (γ- TMT-1 and γ- TMT-2). Both mapped to linkage group 8, cosegregated with the g locus, and were transcribed in developing seeds of wildtype lines. The g mutation greatly decreased γ -TMT-1 transcription, caused alternative splicing of γ -TMT-1, disrupted γ- TMT-2 transcription, and knocked out one of two transcription initiation sites identified in the wildtype; γ- TMT transcription was 36 to 51-fold greater in developing seeds of wildtype ( g ⁺ g ⁺) than mutant ( g g) lines. F₂ populations (B109 × LG24 and R112 × LG24) developed for mapping the g locus segregated for a previously unidentified locus ( d). B109, R112, and LG24 were homozygous for a null mutation ( m = Tph ₁) in MT-1, one of two 2-methyl-6-phytyl-1,4-benzoquinone/2-methyl-6-solanyl-1,4-benzoquinone methyltransferase ( MPBQ/MSBQ-MT) paralogs identified in sunflower. The d mutations segregating in B109 × LG24 and R112 × LG24 were allelic to a cryptic mutation identified in the other MPBQ/MSBQ-MT paralog ( MT-2) and disrupted the synthesis of α- and γ-tocopherol in F₂ progeny carrying m or g mutations— m m g ⁺ g ⁺ d d homozygotes accumulated 41.5% α- and 58.5% β-T, whereas m m g g d d homozygotes accumulated 58.1% γ- and 41.9% δ-T. MT-2 cosegregated with d and mapped to linkage group 4. Hence, novel tocopherol profiles are produced in sunflower seed oil by three non-allelic epistatically interacting methyltransferase mutations. [ABSTRACT FROM AUTHOR]