Identification of genes that contribute to drought tolerance in Populus

Populus species and derived hybrids are valued for their fast growth and are cultivated all over the Northern hemisphere. They are grown primarily for pulp, paper and oriented strand board production. Fast growing poplar also has potential to be used for carbon sequestration as well as a feedstock for the carbon-neutral production of energy. Many of the commonly used species and hybrids are, however, regarded as drought sensitive, which poses a problem for large-scale cultivation, particularly in light of climate change-induced drought spells in areas of poplar growth including the Canadian prairies. To evaluate the extent of drought tolerance variation in commercially important Canadian poplar hybrids, we tested their ability to withstand drought and ranked them based on a series of physiological and morphological responses. Gene expression analysis of the response to drought in the least and most tolerant clones revealed differences in abscisic acid-mediated signaling, in particular a putative negative and a putative positive regulator of this pathway. Thereafter, we tested the functional importance of these two genes by transformation experiments. Overexpression of the putative negative regulator led to reduced drought tolerance in transgenic Arabidopsis thaliana, whereas overexpression of the putative positive regulator led to improved drought tolerance in transgenic Arabidopsis thaliana and transgenic poplars. Taken together, we have generated a better understanding of drought tolerance in available fast-growing poplar hybrids, functionally characterized two poplar genes, and identified strong candidate genes for targeted improvement of drought tolerance in poplar hybrids.