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 alpha-tocopherol (vitamin E). The g = Tph(2) mutation disrupts the synthesis of alpha-tocopherol, enhances the synthesis of gamma-tocopherol, and was predicted to knock out a gamma-tocopherol methyltransferase (gamma-TMT) necessary for the synthesis of alpha-tocopherol in sunflower seeds--wildtype (g(+) g(+)) lines accumulated > 90% alpha-tocopherol, whereas mutant (g g) lines accumulated > 90% gamma-tocopherol. We identified and isolated two gamma-TMT paralogs (gamma-TMT-1 and gamma-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 gamma-TMT-1 transcription, caused alternative splicing of gamma-TMT-1, disrupted gamma-TMT-2 transcription, and knocked out one of two transcription initiation sites identified in the wildtype; gamma-TMT transcription was 36 to 51-fold greater in developing seeds of wildtype (g(+) g(+)) than mutant (g g) lines. F(2) populations (B109 x LG24 and R112 x 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 x LG24 and R112 x LG24 were allelic to a cryptic mutation identified in the other MPBQ/MSBQ-MT paralog (MT-2) and disrupted the synthesis of alpha- and gamma-tocopherol in F(2) progeny carrying m or g mutations--m m g(+) g(+) d d homozygotes accumulated 41.5% alpha- and 58.5% beta-T, whereas m m g g d d homozygotes accumulated 58.1% gamma- and 41.9% delta-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.
Hass
Catherine G
CG
Department of Crop and Soil Science, Oregon State University, Corvallis, OR 97331, USA.
Tang
Shunxue
S
Leonard
Scott
S
Traber
Maret G
MG
Miller
Jerry F
JF
Knapp
Steven J
SJ
D000483:Alleles; D001483:Base Sequence; D020090:Chromosome Segregation; D004843:Epistasis, Genetic; D018506:Gene Expression Regulation, Plant; D005838:Genotype; D006368:Helianthus / Q000201:enzymology / Q000235:genetics*; D008780:Methyltransferases / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid; D024505:Tocopherols / Q000378:metabolism*; D014158:Transcription, Genetic
D008780:Methyltransferases; C047259:gamma-tocopherol methyltransferase; D024505:Tocopherols