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Title: Genetic basis for genotype-environment interactions influencing flavonoid gene expression in Capsicum

Author
item LIGHTBOURN, GORDON - VA POLYTEC INST & ST UNIV
item GRIESBACH, ROBERT - ARS, FNPRU
item Stommel, John

Submitted to: Molecular Genetics and Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2007
Publication Date: 11/1/2007
Citation: Lightbourn, G., Griesbach, R., Stommel, J.R. 2007. Genetic basis for genotype-environment interactions influencing flavonoid gene expression in Capsicum. Molecular Genetics and Genomics. 132:824-829.

Interpretive Summary: Many visible characteristics in plants such as color are the outcome of a biosynthetic pathway. Two types of genes are involved in the expression of a biosynthetic pathway. Structural genes provide the information to create the enzymes that are responsible for each step in the pathway. Regulatory genes control whether the structural genes are turned on or off. We have developed a model system using a pepper plant with black leaves to study how regulatory genes control the function of structural genes for the anthocyanin biosynthetic pathway. Anthocyanins are the pigments responsible for purple to black color in pepper. Growth conditions change pigmentation and hence product quality. We grew plants under various temperature and light conditions and measured pigment content and how genes functioned under these different growing conditions. Under low light conditions, very little leaf anthocyanin pigmentation occurred in contrast with pigmentation observed under high light conditions. Temperature, under either low or high light conditions, had no effect on anthocyanin pigmentation. We identified the specific regulatory gene responsible for this response. This information on anthocyanin content and genes that influence anthocyanin content will facilitate the development and production of novel leaf, stem and fruit colors in pepper and other food crops and ornamentals where color contributes to product quality.

Technical Abstract: Chlorophylls, carotenoids, flavonoids and betalains contribute to color in economically important vegetables, fruits and floral crops. The flavonoids can be subdivided into anthocyanins and co-pigments. Anthocyanin production is markedly influenced by numerous environmental factors including temperature and light stress. The objective of this study was to determine the genetic basis for differences in Capsicum anthocyanin content in response to varying environments. Growth experiments under controlled environment conditions demonstrated that there was a significantly higher anthocyanin concentration in mature leaves in comparison to young leaves under high light (435 'mol s-1m-2) conditions and that high (30oC day/25oC night) vs. low (20oC day/15oC night) temperature had no significant effect on anthocyanin concentration regardless of leaf maturity stage. Foliar anthocyanin concentration from plants grown under short days (10 hours) with low light intensity (215 'mol s-1m-2) was significantly less than under long days (16 hours) with low light. Under high light intensity, daylength had no effect on anthocyanin content. Three structural genes (chalcone synthase, Chs; dihydroflavanoid reductase, Dfr; anthocyanin synthase, Ans) and three regulatory genes (MybAn2; MycAn1; Wd40An11) were selected for comparison under inductive and non-inductive anthocyanin producing conditions. Chs, Dfr and Ans expression was significantly higher in mature leaves in comparison to young leaves. Under both low and high temperatures, expression of Chs, Dfr, and Ans was up-regulated in leaves under high light conditions. Consistent with anthocyanin concentration, under low or high light conditions, temperature had no effect on gene expression. Under all temperature and light conditions evaluated, MycAn1 and Wd40An11 had a constant level of expression. MybAn2, however, was differentially expressed in concert with the structural genes, indicating its role as a transcription factor responsible for regulating anthocyanin structural gene expression in response to different environments. Our gene expression studies provide evidence that transcription factor x structural gene interaction account for phenotypic variation that results from the joint action of the genotype and environment.