Scientists at Tokyo Institute of Technology (Tokyo Tech) have identified two
proteins that help plants respond to changing light conditions, making
photosynthesis more efficient. Photosynthesis need sunlight to proceed.
Proteins involved in this process need to be 'on' in the presence of
sunlight, but needs to be idle when it is dark and photosynthesis is not
possible.

This is done through a process called 'redox regulation'-the activation and
deactivation of proteins via changes in their redox states. What happens in
the presence of light is well understood: the ferredoxin-thioredoxin
reductase (FTR)/thioredoxin (Trx) pathway is responsible for the reduction
process, which activates the photosynthetic pathway. However, scientists
have long been in the dark about what happens in the absence of light, and
how plants reset photosynthetic proteins to be ready to function when light
is resumed.

Keisuke Yoshida, Toru Hisabori, and colleagues identified two proteins,
constituting the thioredoxin-like2 (TrxL2)/2-Cys peroxiredoxin (2CP) redox
cascade, that help control the reoxidation of these photosynthetic proteins
by modifying key parts of the molecular players.

These two proteins appear to function as part of a cascade that draws energy
from the photosynthetic proteins to the always energy-hungry hydrogen
peroxide. TrxL2 seems to be specialized for the 'switching off' process.
TrxL2 is an efficient oxidizer of many proteins, but only reduces 2CP,
allowing the energy drained by TrxL2 from several upstream reactions to pass
to 2CP and thence hydrogen peroxide. This cascade thus keeps photosynthesis
on standby until light is available again.

[www.titech.ac.jp]