Gene Expression Profiles of Low Temperature Related Genes in Cold Resistant and Sensitive Black Poplar (Populus nigra L.) Clones

Low temperature is one of the major environmental constraint which affect  the survival of  woody plants. Black poplar (Populus nigra) has a broad diversity of proteomic, biochemical and physiological mechanisms to cope with low temperature effects. Low temperature not only induces  different types of responses, but also, it triggers many pathways that bring about differential gene expression in black poplar. In this study, four important time/temperature points were selected to identify the low temperature induced genes in cold resistant and cold sensitive black poplar clones by using microarray techniques. The stem sections were collected in  September 2011 (19.32°C) as control, in November 2011 (before cold: 1.61°C), in February 2012 (during cold: -2.53°C) and  in April 2012 (after cold: 13.76°C). The differential expression of low temperatures related genes were examined in these four period. A statistical threshold for the microarray data analysis detected a total of 3983 genes significantly expressed (Fold Change (FC)≥5, p value≤0.01) in cold resistant clones. Among these genes, 1649 were significantly expressed on February, about 650 of these were up regulated  while over 1000 of  them were down regulated in cold resistant clone. In cold sensitive clone, 3732 genes were differentially expressed and 1817 of them with similar pattern as in cold resistant clone were significantly expressed on February 2012. In contrast to differentially altered genes in the resistant genotype, low temperature had more impact on the transcriptome of the sensitive genotype. In November, carbohydrate metabolism seems to be important for black poplar clones for preparing themselves to winter conditions while in February, carbohydrate metabolism and transport activity related genes were expressed. On the other hand,  genes related to resonse to cold were highly expressive in cold sensitive clone. Information generated from this study provides new data on list of possible candidate genes involved in cold response in black poplars that could be  highly useful for future studies dealing with mechanisms of chilling tolerance in woody plants.