Introduction of a novel pathway for IAA biosynthesis to rhizobia alters vetch root nodule development
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ORIGINAL PAPER
Introduction of a novel pathway for IAA biosynthesis to rhizobia alters vetch root nodule development Serena Camerini · Beatrice Senatore · Enza Lonardo · Esther Imperlini · Carmen Bianco · Giancarlo Moschetti · Giuseppe L. Rotino · Bruno Campion · Roberto Defez
Received: 5 June 2007 / Revised: 22 January 2008 / Accepted: 17 March 2008 / Published online: 16 April 2008 © Springer-Verlag 2008
Abstract We introduced into Rhizobium leguminosarum bv. viciae LPR1105 a new pathway for the biosynthesis of the auxin, indole-3-acetic acid (IAA), under the control of a stationary phase-activated promoter active both in free-living bacteria and bacteroids. The newly introduced genes are the iaaM gene from Pseudomonas savastanoi and the tms2 gene from Agrobacterium tumefaciens. Free-living bacteria harbouring the promoter-iaaMtms2 construct release into the growth medium 14-fold more IAA than the wild-type parental strain. This IAA overproducing R. l. viciae, the RD20 strain, elicits the development of vetch root nodules
containing up to 60-fold more IAA than nodules infected by the wild-type strain LPR1105. Vetch root nodules derived from RD20 are fewer in number per plant, heavier in terms of dry weight and show an enlarged and more active meristem. A signiWcant increase in acetylene reduction activity was measured in nodules elicited in vetch by RD20. Keywords IAA · ARA · Auxin · Nitrogen Wxation · Nodule zone · Vicia hirsuta
Introduction Communicated by Ursula Priefer. S. Camerini · B. Senatore · E. Lonardo · E. Imperlini · C. Bianco · R. Defez (&) Institute of Genetics and Biophysics, CNR, via P. Castellino 111, 80131 Naples, Italy e-mail: [email protected] G. Moschetti SENFIMIZO, Università di Palermo, Palermo, Italy G. L. Rotino · B. Campion CRA-ISPORT, Research Institute for Vegetable Crops, Montanaso Lombardo (LO), Italy Present Address: S. Camerini Istituto Superiore di Sanità, viale Regina Elena, 299, 00161 Rome, Italy Present Address: B. Senatore Dipartimento di Ingegneria chimica alimentare, Università di Salerno, Fisciano (SA), Italy Present Address: E. Imperlini IRCSS, Fondazione SDN via Gianturco, 113, 80143 Naples, Italy
Research on phytohormones is a very old Weld of investigation. Charles Darwin performed phototropism experiments in which demonstrated the presence of a transported signal originating from the plant apex, able to promote diVerential cell elongation in the seedling lower parts resulting in its bending toward the light source (Darwin and Darwin 1880). This signal was subsequently isolated and named auxin by Went (1935). Thimann in 1936 proposed that auxins, such as indole-3-acetic acid (IAA) play a role in root nodule organogenesis. Nitrogen-Wxing rhizobia enter into symbiosis with (mainly) leguminous plants eliciting root nodule development triggered by the Nod factor (Stougaard 2000). Symbiotic nitrogen Wxation represents the main naturally occurring mechanism by which atmospheric nitrogen is reduced (Brill 1977). Several lines of evidence suggest a role for phytohormones in
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