Expression profiling of cold-induced hybrid necrosis in triploid hybrids crossed between tetraploid wheat and Aegilops tauschii.

We have employed whole genome microarray expression profiling as a discovery platform to identify genes to alter the transcript accumulation levels in cold-induced hybrid necrosis lines, which are triploid hybrids crossed between tetraploid wheat and diploid wheat progenitor Aegilops tauschii. Of the up-regulated genes, defense-related genes were most frequently found in the leaves and shoot apical meristem (SAM) of type II necrosis line with low temperature. On the other hand, cell cycle-related genes were highly down-regulated in SAM of type II necrosis line under low temperature. To validate the microarray data, RT-PCR and quantitative RT-PCR analyses for 37selected genes were performed in total. Of the examined 21 up-regulated and 16 down-regulated genes, more than 75% of expression pattern were consistent with the microarray data. Together with cytological analysis of the necrotic tissues, the microarray analysis strongly suggests that an autoimmune response-like reaction and repression of cell division might be triggered by intergenomic incompatibility between the AB and D genomes in type II necrosis. Expression patterns were compared between the two synthetic hexaploid lines showing the wild-type phenotype (as a reference) and cold-induced hybrid necrosis. Total RNA samples were isolated from the 3-week-old seedling leaves. In addition, total RNA were also extracted from the seedling leaves and shoot meristem with 12- and 6-weeks of low temperature, respectively. Two independent experiments were conducted in each exprement.