Gene expression analysis in response to low and high temperature and oxidative stresses in rice: combination of stresses evokes different transcriptional changes as against stresses applied individually.

Transcript expression profiles of rice seedlings were analyzed in response to (a) prior exposure with oxidative stress followed by heat or cold stress and (b) simultaneous exposure to oxidative stress along with heat stress or cold stress. The numbers of genes differentially regulated during stress combination of cold and oxidative stress as well as heat and oxidative stress treatments were higher when compared with the number of genes differentially regulated in response to individual stress conditions. A large number of transcript changes were noted unique to the stress combination mode as compared with when individual stresses were applied. Specific differences in the transcript expression profiles of OsHsf and OsClp gene family members were noted during combination of stresses as against individual stresses. For instance, OsHsf26 induction was specific to stress combinations, while OsHsfA2a, OsHsfA2f, and OsHsfA3 transcript levels were additively affected during combination of stresses. Unique promoter models and transcription factor binding sites (i.e. P$KNOX3_01, P$OSBZ8_Q6) were noted in the promoters of differentially regulated genes during combination of stresses. It is proposed that stress combinations represent a novel state of abiotic stresses for rice seedlings that might involve a different type of molecular response.