Identification of nitrogen responsive genes in poplar roots grown under two contrasting nitrogen levels

We investigated the short-term response of poplar roots to low and high nitrogen availability in order to elucidate the mechanisms involved in nutrient acquisition. After 28 days of fertilization with low versus high ammonium nitrate, an increase in aboveground biomass was observed accompanied by a decrease in root biomass, reducing the root: shoot ratio after 28 days. These changes in biomass allocation were accompanied by changes in root architecture and altered gene expression. The gene expression response was evaluated after 7 days using a custom cDNA micrarray following transfer to low and high nitrogen supply. We found that 56 sequences were differentially expressed in poplar roots. Many of these 56 genes could be associated with putative roles in development or response to biotic and abiotic stress. A time course analysis of selected cell wall-related genes by RT-qPCR confirmed the expression patterns obtained by microarray and also showed the timing of this differential response. Our results show that patterns of transcript accumulation in roots of poplars are influenced by nitrogen supply, providing evidence of unique nitrogen-adaptative mechanisms.