Further work now in progress aims to increase the provitamin
A amount by identifying the metabolic rate-limiting
bottlenecks in Golden Rice. New transformations are underway
using different endosperm-specific promoters, a codonoptimized
crtI-gene and early pathway genes of the so-called
nonmevalonate pathway of isoprenoid biosynthesis (13). Further
proof-of-concept work aiming to measure and enhance
the bioavailability and bioefficacy of provitamin A are underway.
One further approach aims to unify high-iron rice lines
with provitamin A lines because it is known that provitamin
A is capable of increasing the bioavailability of iron.