When light governs gene expression
Initially characterised in plants some forty years ago, phytochromes were first discovered only five years ago in bacteria. Phytochromes are present in two forms, one active and the other inactive, which absorb light in either the red or the near infrared ranges. According to the illumination, the phytochrome changes from one form to the other and then sets off a sequence of biochemical events causing, for example, germination or growth in the plant. The phytochrome thus acts as a light-operated switch. However, the function of bacterial phytochromes was unclear.
The results obtained by the two teams concerned, a mixed CEA-CNRS unit and a team from the IRD, display two main novel aspects, First the researchers have, for the first time, identified the process activated by this new phytochrome together with all the different associated molecules involved in this regulation. Second, the results reveal a new type of phytochrome. Its mode of regulation relies on a simple protein-protein interaction (with a specific protein responsible for the expression of certain genes), with no chemical modification, unlike the cytochromes known to date, whose activation mechanism involves changes in the phosphorylation state of certain amino acids.
The discovery of the mechanism of action of this new type of phytochrome makes it possible to envisage the activation or inhibition of the synthesis of certain target genes simply by controlling light exposure. Most current systems, which are still at the experimental stage, use a chemical inducer, but they lack flexibility and are not readily reversible. The specific features of this new photo-activated regulation mechanism suggests many possible applications, from the study of certain protein functions to gene therapy.
Référence :
Nature 417, 202 - 205 (2002)
Bacteriophytochrome controls photosystem synthesis in anoxygenic bacteria
ERIC GIRAUD*, JOËL FARDOUX*, NICOLAS FOURRIER*, LAURE HANNIBAL*, BERNARD GENTY†, PIERRE BOUYER‡, BERNARD DREYFUS* & ANDRÉ VERMÉGLIO‡
* LSTM TA 10/J Laboratoire des Symbioses Tropicales et Méditerranéennes, UMR 113, IRD/CIRAD/INRA/ENSA-M. Campus de Baillarguet, 34398 Montpellier Cedex 5, France
† CEA/Cadarache DEVM-Laboratoire d'Écophysiologie de la Photosynthèse, UMR 163-CNRS-CEA, 13108 Saint Paul lez Durance Cedex, France
‡ CEA/Cadarache DEVM-Laboratoire de Bioénergétique Cellulaire, UMR 163-CNRS-CEA, Univ-Méditerranée CEA1000, 13108 Saint Paul lez Durance Cedex, France
Press contacts
CEA – Pascal Newton – Tél : 01 40 56 20 97 – pascal.newton@cea.fr
IRD – Hélène Deval ou Marie-Lise Sabrié, - Tél : 01 48 03 75 19 - deval@paris.ird.fr
CNRS – Martine Hasler – Tél : 01 44 96 46 35 – martine.hasler@cnrs-dir.fr