Replacement of chloroplast ferredoxin with a bacterial flavodoxin leads to enhanced tolerance to iron starvation in tobacco

ZURBRIGGEN M; TOGNETTI V; HAJIREZAEI MR; VALLE E; CARRILLO N

Seoul, South Korea

Conferencia; XIX FAOBMB Seoul Conference (Federation of Asian and Oceanian Biochemists and Molecular Biologists); 2007

Federation of Asian and Oceanian Biochemists and Molecular Biologists), Seoul, South Korea, Mayo de 2007.

Iron limitation affects one third of the cultivable land on Earth and represents a major concern for agriculture. It causes decline of many photosynthetic components, including the iron-sulfur protein ferredoxin (Fd), involved in essential oxido-reductive pathways of chloroplasts. In cyanobacteria and some algae, Fd down-regulation under iron deficit is compensated by induction of an isofunctional electron carrier, flavodoxin (Fld), an FMN-containing protein not found in plants. Transgenic tobacco lines expressing a cyanobacterial Fld in chloroplasts were able to grow in iron-deficient media that severely compromised survival of wild-type plants. Fld expression did not improve iron uptake or mobilization, and stressed transformants elicited a normal deficit response, including induction of ferric-chelate reductase and metal transporters. However, the presence of Fld did prevent decrease of several photosynthetic proteins and partially protected photosynthesis from inactivation. It also preserved the activation state of enzymes depending on the Fd-thioredoxin pathway, which correlated with higher levels of intermediates of carbohydrate metabolism and the Calvin cycle, as well as increased contents of sucrose, glutamate and other amino acids. These metabolic routes depend, directly or indirectly, on the provision of reduced Fd. The results indicate that Fld could compensate Fd decline during episodes of iron deficiency by productively interacting with Fd-dependent pathways of the host, providing fresh genetic resources for the design of plants able to survive in iron-poor lands.