Rewiring carotenoid biosynthesis in plants using a viral vector

A healthy human diet should include phytonutrients such as carotenoids. Several approaches including classical breeding and transgenic plant production have been used to increase carotenoid abundance in plant tissues; challenges to these approaches include feedback controls, cell toxicity due to abnormally high compound levels, and compartmentalization of enzymes and intermediates. Majer et al. demonstrate high levels of lycopene production in leaf cytosolic tissues by way of a transiently expressed viral vector carrying three enzymes derived from bacteria.  They report an unexpected tissue yellowing in cells expressing just the first enzyme of the pathway, which should accumulate a colorless intermediate; this yellowing they ascribe to chlorosis and decreased accumulation of chlorophyll through an as yet unexplained mechanism. However, this effect can be harnessed as a visual marker to track virus dynamics (stability, replication and movement). Sci. Reports 10.1038/srep41645