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BIOLOGICAL SCIENCES / PLANT BIOLOGY
Enhanced plant tolerance to iron starvation by functional substitution of chloroplast ferredoxin with a bacterial flavodoxin
*Instituto de Biología Molecular y Celular de Rosario, Consejo Nacional de Investigaciones Científicas y Técnicas, and Facultad de Ciencias Agrarias, Universidad Nacional de Rosario, Suipacha, 531, S2002LRK Rosario, Argentina; Bioquímica y Biología Molecular y Celular, Universidad de Zaragoza, Pedro Cerbuna, 12, E-50009 Zaragoza, Spain; and Leibniz-Institut für Pflanzengenetik und Kulturpflanzenforschung, Corrensstrasse 3, D-06466 Gatersleben, Germany
Communicated by Luis Herrera-Estrella, Center for Research and Advanced Studies, Guanajuato, Mexico, May 15, 2007 (received for review February 14, 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 Fe-S protein ferredoxin (Fd), involved in essential oxidoreductive pathways of chloroplasts. In cyanobacteria and some algae, Fd down-regulation under Fe deficit is compensated by induction of an isofunctional electron carrier, flavodoxin (Fld), a flavin mononucleotide-containing protein not found in plants. Transgenic tobacco lines expressing a cyanobacterial Fld in chloroplasts were able to grow in Fe-deficient media that severely compromised survival of WT plants. Fld expression did not improve Fe 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 (but not Fd) 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 Fe deficiency by productively interacting with Fd-dependent pathways of the host, providing fresh genetic resources for the design of plants able to survive in Fe-poor lands.
iron deficiency | redox status | cyanobacteria | transgenics | thioredoxin
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/cgi/content/full/0704553104/DC1.
¶To whom correspondence should be addressed. E-mail: carrillo{at}ibr.gov.ar
© 2007 by The National Academy of Sciences of the USA
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