|Payyavula, Raja -|
Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 12, 2013
Publication Date: November 15, 2013
Citation: Payyavula, R., Navarre, D.A. 2013. Transcription factors, sucrose and sucrose metabolic genes interact to regulate potato phenylpropanoid metabolism. Journal of Experimental Botany. 64:5115-5131. Interpretive Summary: An important class of compounds in potatoes are the phenylpropanoids. These are the major antioxidants in potatoes, can have various health promoting effects and are desirable in the diet. The regulatory mechanisms that control how much of these compounds are found in a given potato cultivar are poorly understood. This work shows that sugars and certain transcription factors play a major role in determining what quantities of phenylpropanoids will accumulate in tubers. Of special interest is the finding that a regulatory loop exists that involves sugars, MYB and bHLH transcription factors and sugar metabolic genes that controls expression of the phenylpropanoid pathway.
Technical Abstract: Much remains unknown about how transcription factors and sugars regulate phenylpropanoid metabolism in tuber crops like potato. Based on phylogeny and protein similarity, 15 transcription factors were selected and their expression was compared in white, yellow, red and purple genotypes with contrasting phenolic and anthocyanin profiles. Red and purple genotypes had increased PAL enzyme activity, markedly higher levels of phenylpropanoids and elevated expression of most phenylpropanoid structural genes, including a novel anthocyanin O-methyltransferase. Anthocyanin1 (StAN1), basic Helix Loop Helix1 (StbHLH1) and StWD40 were more strongly expressed in red and purple potatoes. Expression of 12 other transcription factors was not associated with phenylpropanoid content, except for StMYB12B, which showed a negative relationship. Increased expression of AN1, bHLH1 and WD40 was also associated with environmentally mediated increases in tuber phenylpropanoids. Treatment of potato plantlets with sucrose induced hydroxycinnamic acids, flavonols, anthocyanins, structural genes, AN1, bHLH1, WD40 and genes encoding the sucrose hydrolyzing enzymes, SUSY1, SUSY4 and INV2. Transient expression of StAN1 in tobacco leaves induced bHLH1, structural genes, SUSY1, SUSY4 and INV1 and increased phenylpropanoid amounts. StAN1 infiltration decreased sucrose and glucose concentrations. In silico promoter analysis revealed the presence of MYB and bHLH regulatory elements on sucrolytic gene promoters and sucrose responsive elements on the AN1 promoter. These findings reveal an interesting dynamic between AN1, sucrose, and sucrose metabolic genes in modulating potato phenylpropanoids.