Proceedings of the XLVII Italian Society of Agricultural Genetics - SIGA Annual Congress

Verona, Italy - 24/27 September, 2003

ISBN 88-900622-4-X

Oral Communication Abstract - S1b

HOW TO KILL TWO BIRDS WITH ONE STONE: ACTIVATION OF THE MYBLEU-REGULATED PATHWAY ALLOWS RICE TO TOLERATE AND ESCAPE ANOXIA

C. VANNINI*, M. BRACALE*, M. MARSONI*, F. LOCATELLI**, S. MANCUSO***, F. FAORO****, A. GENGA**, I. CORAGGIO**

*) Dipt di Biologia Strutturale e Funzionale, Università dell’Insubria, via J.H. Dunant 3, 21100 Varese, Italy

**) Istituto di Biologia e Biotecnologia Agraria, C.N.R., via E. Bassini 15, 20133, Milano, Italy

***) Dipt. Ortoflorofrutticoltura-UniFI, viale delle Idee 30, 50090 Sesto Fiorentino (FI)

****) Istituto di Virologia Vegetale, CNR, via Celoria 2, 20133 Milano, Italy

Mybleu is a natural incomplete transcription factor of rice, consisting of a partial Myb repeat followed by a short leucin zipper. In rice, its presence is restricted to the apical region of roots and coleoptiles. We previously demonstrated its ability to dimerize with canonical leucin zipper and selectively activate transcription. To identify the biological function of Mybleu, we constitutively expressed the Mybleu coding sequence under the control of the constitutive CaMV35S promoter in transformed A. thaliana plants. The localization in the apical region and the expression in both aerobic and anaerobic conditions in rice coleoptiles, and only in aerobic conditions in roots, suggested a Mybleu involvement in cellular differentiation and/or elongation. According to its putative role in cell elongation in the differentiation zone, its constitutive expression induces a change in the root apex morphology. Mybleu expression in A. thaliana, dramatically increases hypoxia tolerance, measured both as survival and ability to germinate. One of the most toxic effects of anoxia/hypoxia depends on the lowering of the cellular pH; on the other hand cell elongation is mediated by H⁺ extrusion in the cellular wall. According, we supposed a Mybleu role in the proton pump function at low oxygen concentration. Actually, measuring the ionic fluxes at several O₂ concentrations, we demonstrated the ability of Mybleu expressing plant to preserve pump functionality (K⁺ and H⁺) at low oxygen pressure. We also demonstrated the ability of the Mybleu expressing transgenic plants, in contrast with the wild type, to elongate under hypoxia. Finally we assayed the energetic charge in wt and transformed plants in aerobic and hypoxic conditions.

Mybleu is the first and up to now the only gene able to confer tolerance to low oxygen condition. Its ability to confer both hypoxia tolerance and ability to growth in limiting oxygen environments suggests that it is a key component in the rice coleoptile peculiarity to survive and grow in submerged soil up to the air.