Université de Strasbourg

Provitamin A

Improved Provitamin A accumulation and stabilisation

USIAS Fellows: Peter Beyer and Philippe Hugueney

Directly or indirectly, all of the vitamin A consumed by humans derives from plants in the form of provitamin A (ß-carotene). Vitamin A deficiency is a major public health problem in developing countries leading to vitamin A deficiency diseases with the consequence of blindness, morbidity and mortality. Therefore, current international projects aim at increasing the provitamin A content in crop plants, this approach also being referred to as biofortification. Frequently, crop plant tissues cannot be improved for this trait by classical breeding because of a lack of trait variability. Rice is an example where genetic modification needed to be employed (Golden Rice) while in maize, for instance, breeding for increased provitamin A carotenoids is feasible.
The teams of Prof. Peter Beyer (Albert-Ludwigs Universität Freiburg, ALUF) and Philippe Hugueney (INRA-Université de Strasbourg) have decided to collaborate since each has identified catalytically improved versions of two enzymes acting at known rate-limiting steps in isoprenoid (including carotenoid) biosynthesis. This relates to the enzyme deoxyxylulose phosphate synthase (DXS), for which INRA-UdS has recently characterized natural DXS alleles in grapevine (Vitis vinifera), which are responsible for the massive accumulation of isoprenoid-derived aroma compounds in Muscat and Gewurztraminer grapes and wines. Each of these highly efficient alleles carry a single mutation affecting key amino acids conserved in all plant DXS. Similarly, ALUF has very effective versions of phytoene synthase (PSY) in hands, stemming from maize and from cassava (caused by a single mutation, like with DXS) providing a strong pathway “push”, when expressed.
Evidently, the combination of both favorable enzymes can be expected to boost carotenoid accumulation. The combined actions of both shall be investigated in non-green cells of model systems such as Arabidopsis thaliana and investigated further in the edible part of the rice grain (endosperm). These studies will be accompanied by enzymological and structural investigations to elucidate the molecular bases of the unusual effectiveness of these enzymes.
The two teams are thus proposing a proof-of-concept, which bears the potential of paving the way for future improvement of provitamin A biofortifed crops, applicable to both marker-assisted breeding and genetic modification.

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