Multilevel interactions between native and ectopic isoprenoid pathways affect global metabolism in rice

Isoprenoids are natural products derived
from isopentenyl diphosphate (IPP) and dimethylallyl
diphosphate (DMAPP). In plants, these precursors
are synthesized via the cytosolic mevalonate (MVA)
and plastidial methylerythritol phosphate (MEP)
pathways. The regulation of these pathways must
therefore be understood in detail to develop effective
strategies for isoprenoid metabolic engineering. We
hypothesized that the strict regulation of the nativeMVA pathway could be circumvented by expressing
an ectopic plastidial MVA pathway that increases ectopic plastidial MVA pathway enhanced the expression
of endogenous cytosolic MVA pathway genes
while suppressing the native plastidial MEP pathway,
increasing the production of certain sterols and tocopherols.
Plants carrying the ectopic MVA pathway
only survived if WR1 was also expressed to replenish
the plastid acetyl-CoA pool. The transgenic plants
produced higher levels of fatty acids, abscisic acid,
gibberellins and lutein, reflecting crosstalk between
phytohormones and secondary metabolism.
the accumulation of IPP and DMAPP in plastids.
We therefore introduced genes encoding the plastidtargeted
enzymes HMGS, tHMGR, MK, PMK and
MVD and the nuclear-targeted transcription factor
WR1 into rice and evaluated the impact of their
endosperm-specific expression on (1) endogenous
metabolism at the transcriptomic and metabolomic
levels, (2) the synthesis of phytohormones, carbohydrates
and fatty acids, and (3) the macroscopic phenotype
including seed morphology. We found that the