Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: August 2, 2007
Publication Date: August 16, 2007
Citation: Lightbourn, G., Stommel, J.R., Griesbach, R.J. 2007. Regulation of Anthocyanin gene expression in capsicum: A member of the Solanaceae family. Meeting Abstract, p.32.
Interpretive Summary: Not Applicable (Meeting Abstract)
Color in seed, flowers, fruit or foliage is attributed to compounds of the flavonoid pathway and chlorophyll, caretonoids and betalains. The flavonoid pathway can be divided into two major branches, copigments (colorless) and anthocynanins (colored). The first structural gene of the enzyme branching from the general phenylpropanoid pathway is chalcone synthases (Chs). Through a number of colorless intermediate molecules, inclusive of substrate for the enzyme dihydroflavonol-4-reductase (Dfr), a colored product is formed by the enzyme anthocyanidin synthase (Ans). Additional enzymes further modifiy (glycosylate) the anthocyanins. A transcription factor complex consisting of MYB, MYC and WD40 control expression of these anthocyanin structural genes. MYB belongs to a R2 R3-domain gene family. The MYC gene family encodes a basic helix-loop-helix domain protein with an N-terminal region rich in basic amino acids and a C-terminal region high in acidic amino acids. The WD40 family contains a tryptophan and aspartic acid repeat sequence.
To ascertain expression levels, we examined foliage, flowers and fruit of green and black pigmented genotypes, representing two contrasting genotypes. We evaluated the expression of the anthocyanin structural genes Chs, Dfr and Ans and the anthocyanin regulatory genes Myb, Myc and Wd40. Realtime PCR analysis of structural gene transcription revealed up-regulation of Chs, Dfr and Ans in all black tissue types. With the exception of Wd40, regulatory gene transcript level differed according to tissue. Fruit and flowers showed differential expression, with sharply elevated levels in black tissue, mirroring structural genes. There was no differential expression of Myb and Myc in black vs. green pigmented leaves; contrasting with differential expression observed in structural genes for leaf tissue. Sequence analysis of leaf tissue revealed two Myb products; green tissue produced a major product where the open reading frame (ORF) was interrupted by an intron. In contrast, black tissue produced a single uninterrupted transcript. Sequence analysis of leaf tissue revealed two Myc forms, both had identical ORFs but differed in the untranslated terminal 3’ends. Fruit and flowers are being similarly evaluated. In leaf tissue where differential structural gene expression was not reflected in regulatory genes, miRNA activity is proposed as a possible regulatory mechanism.