Engineering Secondary Metabolism in Maize Cells by Ectopic Expression of Transcription Factors

Abstract

Manipulation of plant natural product biosynthesis through genetic engineering is an attractive but technically challenging goal. Here, we demonstrate that different secondary metabolites can be produced in cultured maize cells by ectopic expression of the appropriate regulatory genes. Cell lines engineered to express the maize transcriptional activators C1 and R accumulate two cyanidin derivatives, which are similar to the predominant anthocyanin found in differentiated plant tissues. In contrast, cell lines that express P accumulate various 3-deoxy flavonoids. Unexpectedly, P-expressing cells in culture also accumulate phenylpropanoids and green fluorescent compounds that are targeted to different subcellular compartments. Two endogenous biosynthetic genes (c2 and a1, encoding chalcone synthase and flavanone/dihydroflavonol reductase, respectively) are independently activated by ectopic expression of either P or C1/R, and there is a dose-response relationship between the transcript level of P and the degree to which c2 or a1 is expressed. Our results support a simple model showing how the gene encoding P may act as a quantitative trait locus controlling insecticidal C-glycosyl flavone level in maize silks, and they suggest how p1 might confer a selective advantage against insect predation in maize.

Regulation of plant secondary metabolism and associated specialized cell development by MYBs and bHLHs

“…A MYB-bHLH-WD40 complex consisting of subgroup 5 MYB ZmC1 or ZmPL1, subgroup 3F bHLH ZmR or ZmB, and the WD40 protein ZmPAC1 activates early biosynthetic genes that are shared by all of the flavonoid pathways (e.g., CHS, chalcone isomerase [CHI], flavanone 3-hydroxylase [F3H] and dihydroflavonol 4-reductase [DFR] genes) as well as genes that are specific for the anthocyanin pathway (e.g., anthocyanidin synthase [ANS] and UDP-glucose flavonoid 3- O -glucosyltransferase [UFGT] genes) (Figure 3; Goff et al, 1990; Roth et al, 1991; Tuerck and Fromm, 1994; Grotewold et al, 1998; Selinger and Chandler, 1999; Walker et al, 1999; Carey 2004). By contrast, the subgroup 7 MYB ZmP1 activates the production of the floral organ-specific 3-deoxyflavonoids, independently of any bHLH and WD40 cofactors (Grotewold et al, 1994).…”

Transporters in plant sulfur metabolism

“…Vesicles involved in the transport of flavonoid-derived compounds have been found in maize and in sorghum cells (Snyder and Nicholson, 1990; Grotewold et al, 1998; Grotewold and Davies, 2008; Figure 2 , transporter 12). It could be further demonstrated that anthocyanins are transported to the cell wall or the vacuole by at least two distinct vesicle trafficking pathways (Lin et al, 2003).…”

Integrated genomics-based mapping reveals the genetics underlying maize flavonoid biosynthesis

“…The much studied Pericarp1 ( P1 ) is an R2R3-MYB transcription factor which can control the accumulation of various phenylpropanoids by activating a subset of flavonoid biosynthetic genes [33, 34]. The C1 like R2R3-MYB and R1 like bHLH interacting factors also activate the pathway [35].…”