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

Verona, Italy - 24/27 September, 2003

ISBN 88-900622-4-X

Poster Abstract - 1.56

NONSYMBIOTIC PLANT HAEMOGLOBINS AND REGULATION OF NITRIC OXIDE SIGNALING

E. ZAGO*, M. PERAZZOLLI*^,**, C. ANZI*, A. MAROCCO**, P. DOMINICI*, M. DELLEDONNE*

*) Università degli Studi di Verona, Dipartimento Scientifico e Tecnologico, Strada Le Grazie 15, 37134 Verona

**) Istituto di Botanica e Genetica Vegetale, Università Cattolica S.C., Via Emilia Parmense 84, 29100 Piacenza

nonsymbiotic plants haemoglobin, nitric oxide, plant defence response

Nitric oxide (NO) is an important signaling molecule regulating gene expression during plant defence responses and in other important physiological processes like seed germination, de-etiolation, senescence and hypoxia. Recent studies demonstrated that NO production is based on nitric oxide synthase (NOS) and nitrate reductase (NR) activities. The mechanisms for removal of this signal are however still unknown.

In different organisms, from bacteria to mammals, haemoglobins (Hb) control NO homeostasis by converting this molecule to nitrate. Also in plants Hb genes have been identified and have been classified into two groups, symbiotic and nonsymbiotic haemoglobins (nsHb). The function of ubiquitous nsHb has not been clearly identified.

Arabidopsis thaliana possesses two nsHb, AHb1 and AHb2 with different expression pattern and oxygen binding properties. AHb1 is induced, in both roots and rosette leaves, by low oxygen levels. Recombinant AHb1 has an high oxygen affinity. AHb2 is expressed at a low level in rosette leaves and is low temperature-inducible. AHb2 has a lower affinity for oxygen than AHb1. AHb1 has been purified to analyse the interaction between NO and nsHb, and a detoxification model has been proposed. AHb1 shows a dioxygenase activity that convert NO to nitrate with a catalytic cycle in presence of NADPH. To investigate this function in vivo, AHb1 was cloned in the constitutive expression vector pBI-121 and Arabidopsis thaliana transgenic plants, with an increased level of AHb1, were generated. Northern and western analysis allowed selection of lines with higher level of AHb1. These transgenic plants with elevated NO detoxification system give the possibility to analyse the involvement of NO in several different physiological condition in order to get deeper inside the NO-dependent expression pattern.