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Development and Growth Regulation

Morphogenesis and Auxin Sensitivity of Transgenic Tobacco with Different Complements of Ri T-DNA ¹

Dipartimento di Genetica e Biologia Molecolare, Università di Roma 'La Sapienza', P. 1e A. Moro 5, 00185 Roma, Italy, Centro per lo Studio degli Acidi Nucleici, C.N.R. c/o Dpt. Genetica e Biologia Molecolare, Università di Roma `La Sapienza', p.1e A.Moro 5, 00185 Roma, Italy, Istituto Botanico dell'Università, via Farini 90, 43100 Parma, Italy

Leaf explants of hairy root tobacco (Nicotiana tabacum) regenerants characteristically differentiate roots from the wound margins on hormonefree medium. The same response can be elicited on normal tobacco by culturing the explants in the presence of auxin. We show here that the spontaneous rooting of transformed plants is neither due to the activity of right T-DNA-borne auxin genes nor to a substantially altered balance of endogenous hormones. Rather, an increased sensitivity to auxin is conferred to transformed cells by the left T-DNA (TL-DNA). Analysis of the morphogenetic behavior of transgenic tobacco plants obtained by transferring segments of TL-DNA cloned in a binary vector system allowed us to pinpoint TL-DNA genes responsible for this increased auxin sensitivity of hairy root tissues. Three genes (open reading frames 10, 11, 12) are responsible for the spontaneous rooting of leaf explants and confer to transgenic plants an exaggerated response to auxin.

³ Present address: Istituto di Radiobiochimica ed Ecofisiologia Vegetali del C.N.R., Monterotondo Scalo 00016 (Roma), Italy.

¹ Partially supported by Fondazione Istituto Pasteur-Fondazione Cenci-Bolognetti, by Consiglio Nazionale delle Ricerche special grant IPRA, subproject 1, paper No. 1570 and by European Economic Community contract BAP-0018-I (S).

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