COMBINING ECOPHYSIOLOGY AND GENOMICS AS A TOOL TO UNRAVEL STRESS RESISTANCE IN POPLAR

¹ Forstbotanisches Institut, University of Goettingen, Buesgenweg 2, Goettingen 37077, Germany

² Institute of Biotechnology, University of Helsinki, Viikinkaari 5, Helsinki FIN-00014, Finland

Because of its stress-tolerance Populus euphratica is a promising species for breeding programmes and as a pioneering species for tree plantations in difficult areas. We combine genomic and ecophysiological methods to provide fundamental knowledge about salinity and drought-resistance in poplar. An a stress-enriched EST-bank has been constructed with various tissues of P. euphratica after exposure to drought, salinity, heavy metals, ozone, and natural stresses. 6000 unique sequences have been used to construct micro arrays in addition to selected genes (ca. 700) for macro arrays (theme filters). These arrays are currently being used for expressing profiling and identification of new candidate genes related to stress responses. The molecular stresses responses are studied in combination with physiological changes. A prominent example is a controlled formation of H2O2 in P. euphratica roots in response to salinity preceding anatomical changes. In contrast, P. x canescens, a salt-sensitive poplar hybrid, shows exacerbated H2O2 formation and tissue degradation. By comparing the molecular responses of sensitive and resistant species, we aim to find out key signaling systems modulating plant stress responses. In addition, we show that P. euphratica has a higher capacity to exclude salt ions from the symplast and to accumulate sodium in the apoplast than other poplar species. Candidate genes involved in ion homeostasis have been identified, have been cloned and currently analysed in transgenic plants. Financial support by the German Science Foundation (PRG) and the European communities (project ESTABLISH) is gratefully acknowledged.