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Abstract:
The circadian clock is known to increase plant growth and fitness, and thought to
prepare plants for photosynthesis at dawn and dusk; whether this happens in nature was
unknown. We transformed the native tobacco, Nicotiana attenuata to silence two core clock
components, NaLHY (irLHY) and NaTOC1 (irTOC1). We characterized growth and light- and dark-
adapted photosynthetic rates (A
c
) throughout a 24 h day in empty vector-transformed (EV), irLHY,
and irTOC1 plants in the field, and in NaPhyA- and NaPhyB1-silenced plants in the glasshouse. The
growth rates of irLHY plants were lower than those of EV plants in the field. While irLHY plants
reduced A
c
earlier at dusk, no differences between irLHY and EV plants were observed at dawn in
the field. irLHY, but not EV plants, responded to light in the night by rapidly increasing A
c
. Under
controlled conditions, EV plants rapidly increased A
c
in the day compared to dark-adapted plants
at night; irLHY plants lost these time-dependent responses. The role of NaLHY in gating
photosynthesis is independent of the light-dependent reactions and red light perceived by NaPhyA,
but not NaPhyB1. In summary, the circadian clock allows plants not to respond photosynthetically
to light at night by anticipating and gating red light-mediated in native tobacco.
