Transcriptional-Metabolic Networks in β-Carotene-Enriched Potato Tubers: The Long and Winding Road to the Golden Phenotype      

Abstract

Vitamin A deficiency is a public health problem in a large number of countries. Biofortification of major staple crops (wheat [Triticum aestivum], rice [Oryza sativa], maize [Zea mays], and potato [Solanum tuberosum]) with b-carotene has the potential to alleviate this nutritional problem. Previously, we engineered transgenic "Golden" potato tubers overexpressing three bacterial genes for b-carotene synthesis (CrtB, CrtI, and CrtY, encoding phytoene synthase, phytoene desaturase, and lycopene b-cyclase, respectively) and accumulating the highest amount of b-carotene in the four aforementioned crops. Here, we report the systematic quantitation of carotenoid metabolites and transcripts in 24 lines carrying six different transgene combinations under the control of the 35S and Patatin (Pat) promoters. Low levels of B-I expression are sufficient for interfering with leaf carotenogenesis, but not for b-carotene accumulation in tubers and calli, which requires high expression levels of all three genes under the control of the Pat promoter. Tubers expressing the B-I transgenes show large perturbations in the transcription of endogenous carotenoid genes, with only minor changes in carotenoid content, while the opposite phenotype (low levels of transcriptional perturbation and high carotenoid levels) is observed in Golden (Y-B-I) tubers. We used hierarchical clustering and pairwise correlation analysis, together with a new method for network correlation analysis, developed for this purpose, to assess the perturbations in transcript and metabolite levels in transgenic leaves and tubers. Through a "guilt-by-profiling" approach, we identified several endogenous genes for carotenoid biosynthesis likely to play a key regulatory role in Golden tubers, which are candidates for manipulations aimed at the further optimization of tuber carotenoid content.

Gene-Metabolite Networks of Volatile Metabolism in Airen and Tempranillo Grape Cultivars Revealed a Distinct Mechanism of Aroma Bouquet Production

“…On the contrary, Airén berries display a “metabolite imbalance” between the primary (lipids, negatively correlated toward all the other pathways) and the secondary (phenylpropanoids, carotenoids, terpenes, which are positively correlated) metabolism. Finally, the evaluation of the “node strength” (ns) (Diretto et al, 2010) which is the average of all the |ρ| of a node, demonstrates that, with the exception of the primaries as well as some other random metabolite, in general all the compounds under investigation take part with the same “weight” in the metabolic shift arising during berry ripening.…”

“…Subsequently, gene-metabolite correlation heat maps and matrices were built and colored using the GENE-E software (http://www.broadinstitute.org/cancer/software/GENE-E/). Finally, correlation networks were performed as previously described (Diretto et al, 2010). …”

How Can Research on Plants Contribute to Promoting Human Health?

“…Since the reporting of Golden Rice, other staple crops on which many depend almost exclusively for their nutrition have been produced enriched in b-carotene, including maize and cassava (Harjes et al, 2008;Welsch et al, 2010;Yan et al, 2010), which have been produced by selective breeding as well as by genetic engineering (Naqvi et al, 2009). Golden phenotypes resulting from enhanced b-carotene content have also been achieved in other crops, such as potato (Diretto et al, 2010), although since these are no longer staple crops providing the bulk or sole source of nutrients to population groups, it is less likely that these will be useful in terms of alleviating vitamin A deficiency.…”

Transgenic Pro-Vitamin A Biofortified Crops for Improving Vitamin A Deficiency and Their Challenges

“…Higher lycopene accumulation in tomato is a result of silenced lycopene β-cyclases [41]. The third strategy, termed sink engineering, regulates carotenoid storage structures to stably store carotenoids [42]. Table 1 summarizes outcomes on transgenic pVA production in the select crops.…”