Changes in carbon allocation and subplastidal amyloplast structures of specialised Ipomoea batatas (sweet potato) storage root phenotypes.

Vitamin A deficiency (VAD) in Low and Medium Income countries remains a major health concern. Ipomoea batatas, orange sweet potato (OSP), is one of the biofortification solutions being implemented by the World Health Organisation (WHO) to combat VAD. However, high provitamin A (β-carotene) content has been associated with a reduction in dry matter, reducing calorific value and having adverse effects on consumer traits. Both starch and carotenoid formation are located in amyloplasts and could potentially compete for the same precursors. Hence, five different sweet potato storage root phenotypes were characterized through spatial metabolomics and proteomics at the sub-plastidal level. The metabolite data suggested an indirect correlation of starch and carotenoids through the TCA cycle and pentose phosphate pathway. Furthermore, a change in lipid composition was observed to accommodate the storage of carotenoids in the hydrophilic environment of the amyloplast. The data suggests an alteration of cellular ultra-structures and perturbation of metabolism in high β-carotene producing sweet potato roots. This corroborates with previous gene expression analysis through biochemical analysis of sweet potato root tissue. Interaction between carotenoid and starch biosynthesis in sweet potato amyloplasts. [Display omitted] • Starch and carotenoids compete for the same metabolite precursors. • Reduction of starch is indirectly linked to carotenoids through pyruvate biosynthesis. • Presence of carotenoids changes the cellular ultra-structures of the plastid. • All membrane structures in the root plastid are derived from the plastid envelope. • Functions of membrane structures include synthesis, transport and storage of carotenoids. [ABSTRACT FROM AUTHOR]