Photosynthesis: The Last Link in the Chain

Plants can switch between linear and cyclic modes of electron transport in order to maintain the appropriate balance between ATP and NADPH. An electron transporter called ferredoxin, which receives electrons directly from PSI, acts as the junction that connects the two. It was therefore proposed that a so-called ferredoxin-plastoquinone  reductase (FQR) must exist, which ensures that electrons can be re-injected into the electron transport chain, and thus allows for cyclic electron transport, but despite intensive searches, no such enzyme had been found.

In 2008, a protein called PGRL1 was identified and it was able to interact with PSI and with other factors known to participate in cyclic electron transport. It turns out that the protein is the long-sought FQR that plays a central role in the regulation of cyclic electron flow. Pivotal regulators such as PGRL1 could be used to enhance the efficiency of photosynthesis and thus increase yields in crop plants grown under controlled conditions.