Synthetic routine of luciferin: footstone of auto-glowing
plants
Here we define “plantern” (a chimera of “plant” and “lantern” in
both semantics and biology) as transgenic plant that is capable to
produce visible light need neither external illumination nor exogenous
substances, and the bioluminescence is bright enough to be observed with
naked eyes. Feasibility of designing “planterns” as streetlights have
been evaluated according to photosynthetic efficiency and luminous
energy output. To produce as much light as tranditional streetlights,
glowing plants have to output more than 1000 lumens by the transformed
firefly bioluminescent system. It was estimated that a fast-grow tree
glowing with the firefly luciferase-luciferin pairs only have to divert
approximately 0.3 % of the stored energy to generate bright-enough
bioluminesence during the nighttime (Reeve et al., 2014). In addition to
producing light, planterns are also leveraged for whole-plant imaging
and studying spatiotemporal expression of genes during the entire
life-cycle, for limitations on delivering exogenous luciferin to the
whole plant and tissue would no longer be a bottleneck (Reuter et al.,
2020).
Rebuilding luciferin biosynthetic routine is the priority of generating
“planterns”, which could be achieved by introducing all genes
associated with luciferin biosynthesis (Krichevsky et al., 2010) or
integrating luciferin biosynthetic routine into native plant metabolic
pathway (Khakhar et al., 2020; Mitiouchkina et al., 2019). In the latter
situation, the complicated biosynthesis pathway could be simplified. The
unclarified intermediate steps would even be skipped if products of the
unknown enzymatic reaction have been found in plant metabolome. Once the
luciferin biosynthetic pathway in plant cells is reconstrcuted, common
plant genetic engineering technique would be used to make the transgenic
glowing plants (Figure 1 ).
Besides those well-known bioluminescent systems that have been
reconstructed in plant metabolome, new bioluminescent systems were also
discovered recently. More alternatives of intracellular illuminants
would be available once unveiling the mysteries of newly-found
bioluminescent systems (Kaskova et al., 2016). Some of these systems
might be suitable for plant cells or whose synthetic pathways could be
reconstituted in plant metabolic routine. Recently, a novel yellow
bioluminescent system from annelid worms in the genus Tomopteris ,
kinds of pelagic polychaetes, was separated and characterized (Glagoleva
et al., 2020). The worm luciferin turned out to be aloeemodin, which had
been also discovered in plants, such as aloe and senna(Heidemann et al., 1996). Arachnocampa luminosa , a New Zealand
luminescent glowworm, can generate blue-green light. The glowworm
luciferase shares 31% sequence identity with firefly luciferase, but
catalyzing an entirely new luciferin whose biosynthetic pathway begins
from xanthurenic acid and tyrosine (Watkins et al., 2018).
Dinoflagellate, notorious protist responsible for causing the surface of
the ocean to sparkle at night, produce bluish-green gimmer under
mechanical disturbance (Valiadi & Iglesias-Rodriguez, 2013). The
dinoflagellate luciferin is believed as derivative of chlorophylla because of their similar molecular structures (Topalov &
Kishi, 2001). Genes associated with reaction converting chlorophylla into dinoflagellate luciferin could be introduced into parts of
chloroplasts when synthetic routine of dinoflagellate luciferin is
clarified.