Ectopic expression of soybean leghemoglobin in chloroplasts impairs gibberellin biosynthesis and induces dwarfism in transgenic potato plants Ana Lucia Bonna Æ Alejandro Chaparro-Giraldo Æ Beatriz Appezzato-da-Gloria Æ Peter Hedden Æ Marcio C. Silva-Filho Received: 28 May 2008 / Accepted: 19 June 2008 / Published online: 5 July 2008 Ó Springer Science+Business Media B.V. 2008 Abstract We have characterized potato (Solanum tuberosum L.) plants expressing a soybean leghemo- globin that is targeted to plastids. Transgenic plants displayed a dwarf phenotype caused by short inter- node length, and exhibited increased tuberization in vitro. Under in vivo conditions that do not promote tuberization, plants showed smaller parenchymal cells than control plants. Analysis of gibberellin (GA) concentrations indicated that the transgenic plants have a substantial reduction (approximately 10-fold) of bioactive GA 1 concentration in shoots. Application of GA 3 to the shoot apex of the transformed plants completely restored the wild type phenotype suggesting that GA-biosynthesis rather than signal transduction was limiting. Since the first stage of the GA-biosynthetic pathway is located in the plastid, these results suggest that an early step in the pathway may be affected by the presence of the leghemoglobin. Keywords Gibberelin Á Dwarfism Á Leghemoglobin Á Plant stature Introduction Introduction of dwarfism into plants is one of the prime targets for crop improvement because it allows better management and higher yields while avoiding lodging in cereals (Hedden 2003). The use of dwarfing genes in wheat and rice breeding dates from the beginning of the 20th century in the far-east and has spread worldwide as a consequence of the Green Revolution. The recognition that Reduced height (Rht) genes of wheat cause impairment of gibberellin (GA) signal transduction (Peng et al. 1999), while the rice semi-dwarf1 (sd1) genes disrupt GA biosynthesis (Monna et al. 2002; Sasaki et al. 2002; Spielmeyer et al. 2002) demonstrate the importance of GAs for the control of plant architec- ture. Thus, genetic manipulation of GA biosynthesis or signal transduction offers a very promising strat- egy for crop improvement (Phillips 2004). A. L. Bonna Á A. Chaparro-Giraldo Á M. C. Silva-Filho (&) Departamento de Gene ´tica, Escola Superior de Agricultura Luiz de Queiroz, Universidade de Sa ˜o Paulo, Av. Pa ´dua Dias 11, Caixa Postal 83, 13400-970 Piracicaba, SP, Brazil e-mail: mdcsilva@esalq.usp.br Present Address: A. Chaparro-Giraldo Departamento de Biologia, Universidad Nacional de Colombia, AA 1440 Santafe de Bogota, Colombia B. Appezzato-da-Gloria Departamento de Cie ˆncias Biolo ´gicas, Escola Superior de Agricultura Luiz de Queiroz, Universidade de Sa ˜o Paulo, Av. Pa ´dua Dias, 11, 13400-970 Piracicaba, SP, Brazil P. Hedden Rothamsted Research, Harpenden, Herts AL5 2JQ, UK 123 Mol Breeding (2008) 22:613–618 DOI 10.1007/s11032-008-9203-5