QTL mapping and molecular characterization of the classical D locus controlling seed and flower color in Linum usitatissimum (flax)

Citation

Sudarshan, G.P., Kulkarni, M., Akhov, L., Ashe, P., Shaterian, H., Cloutier, S., Rowland, G., Wei, Y., Selvaraj, G. (2017). QTL mapping and molecular characterization of the classical D locus controlling seed and flower color in Linum usitatissimum (flax). Scientific Reports, [online] 7(1), http://dx.doi.org/10.1038/s41598-017-11565-7

Plain language summary

Linseed flowers are commonly blue-hued but can vary from white to violet while seeds are typically brown but can also be yellow, olive, black or variegated. Three recessive genes for yellow seed coat were previously identified as B1, D and G. In this research, we mapped and identified the actual D gene responsible for the yellow seed coat of line G1186/94. The D gene encodes a flavonoid hydroxylyase that is responsible for both yellow seed and white flower traits. The difference between the dominant brown seed form and the recessive yellow seed form of the gene was a single amino acid change in the flavonoid hydroxylyase protein caused by a single base change in the DNA. The wild type flavonoid hydroxylase is involved in the production of delphinidin pigment which the modified form can no longer efficiently produce; hence the lack of pigmentation in seed coats and flowers of lines carrying this gene form.

Abstract

The flowers of flax (linseed) are blue-hued, ephemeral and self-pollinating, and the seeds are typically brown. A century-old interest in natural yellow seed variants and a historical model point to recessive alleles in B1, D and G loci being responsible, but the functional aspects had remained unknown. Here, we characterized the "D" locus by quantitative trait loci (QTL) mapping and identified a FLAVONOID 3′5′ HYDROXYLASE (F3′5′H) gene therein. It does not belong to the F3′5′H clade, but resembles biochemically characterized F3′Hs (flavonoid 3′ hydroxylase) but without F3′H activity. The genome lacks other F3′H or F3′H-like genes. The apparent neo-functionalization from F3′H is associated with a Thr498 → Ser498 substitution in a substrate recognition site (SRS). The yellow seed and white flower phenotypes of the classical d mutation was found to be due to one nucleotide deletion that would truncate the deduced product and remove three of the six potential SRS, negatively impacting delphinidin synthesis. Delphinidin is sporadic in angiosperms, and flax has no known pollination syndrome(s) with functional pollinator group(s) that are attracted to blue flowers, raising questions on the acquisition of F3′5′H. The appearance of d allele is suggestive of the beginning of the loss of F3′5′H in this species.

Publication date

2017-12-01

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