Genetic basis of unstable expression of high gamma-tocopherol content in sunflower seeds

Abstract

BackgroundTocopherols are natural antioxidants with both in vivo (vitamin E) and in vitro activity. Sunflower seeds contain predominantly alpha-tocopherol (>90% of total tocopherols), with maximum vitamin E effect but lower in vitro antioxidant action than other tocopherol forms such as gamma-tocopherol. Sunflower germplasm with stable high levels of gamma-tocopherol (>85%) has been developed. The trait is controlled by recessive alleles at a single locus Tph2 underlying a gamma-tocopherol methyltransferase (gamma-TMT). Additionally, unstable expression of increased gamma-tocopherol content in the range from 5 to 85% has been reported. The objective of this research was to determine the genetic basis of unstable expression of high gamma-tocopherol content in sunflower seeds.ResultsMale sterile plants of nuclear male sterile line nmsT2100, with stable high gamma-tocopherol content, were crossed with plants of line IAST-1, with stable high gamma-tocopherol content but derived from a population that exhibited unstable expression of the trait. F2 seeds showed continuous segregation for gamma-tocopherol content from 1.0 to 99.7%. Gamma-tocopherol content in F2 plants (average of 24 individual F3 seeds) segregated from 59.4 to 99.4%. A genetic linkage map comprising 17 linkage groups (LGs) was constructed from this population using 109 SSR and 20 INDEL marker loci, including INDEL markers for tocopherol biosynthesis genes. QTL analysis revealed a major QTL on LG 8 that corresponded to the gamma-TMT Tph2 locus, which suggested that high gamma-tocopherol lines nmsT2100 and IAST-1 possess different alleles at this locus. Modifying genes were identified at LGs 1, 9, 14 and 16, corresponding in most cases with gamma-TMT duplicated loci.ConclusionsUnstable expression of high gamma-tocopherol content is produced by the effect of modifying genes on tph2a allele at the gamma-TMT Tph2 gene. This allele is present in line IAST-1 and is different to allele tph2 present in line nmsT2100, which is not affected by modifying genes. No sequence differences at the gamma-TMT gene were found associated to allelic unstability. Our results suggested that modifying genes are mostly epistatically interacting gamma-TMT duplicated loci.

Genetic Analysis of Reducedγ-Tocopherol Content in Ethiopian Mustard Seeds

“…Loss of function of γ -TMT has resulted in nearly complete replacement of α -tocopherol by γ -tocopherol in sunflower [ 26 ] and safflower [ 27 ]. The opposite situation, that is, increased α -tocopherol and reduced γ -tocopherol relative concentrations, has been reported to occur due to higher activity of the γ -TMT promoter in soybean [ 28 ], to the presence of additional active copies of the γ -TMT gene in sunflower [ 29 ], and also to induction by overexpression of the γ -TMT gene in several species such as Arabidopsis , soybean, and Brassica juncea [ 13 , 30 – 32 ]. The Ethiopian mustard line BCT-6 showed a reduction of total γ -tocopherol content in addition to a change in the relative proportion of α - and γ -tocopherol, which has not been reported in any of the abovementioned studies.…”

Selection for contrasting tocopherol content and profile in Ethiopian mustard

“…García‐Moreno et al. () reported that the presence of several copies of γ‐TMT contributed to α‐tocopherol accumulation in a sunflower mutant in which the main γ‐TMT locus was altered. Further studies are required to elucidate the molecular mechanisms leading to either reduced or increased levels of the α/γ‐tocopherol ratio in the Ethiopian mustard lines developed in the present research.…”

Environmental Stability of Contrasting Seed Tocopherol Profiles in Sunflower

“…High γ‐tocopherol content is produced by recessive alleles at Tph2 whereas high δ‐tocopherol content is the result of epistatic interaction of recessive alleles at the three loci (Hass et al, 2006). A recent molecular analysis revealed that the two lines with high γ‐tocopherol content used in the present research, T2100 and IAST‐1, carry different alleles at the same locus Tph2 (García‐Moreno et al, 2012). In both cases, high γ‐tocopherol content showed high environmental stability, with overall coefficients of variation over 14 environments below 1%.…”