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Rice being an important cereal crop is highly sensitive to salinity stress causing growth retardation and loss in productivity. However, certain rice genotypes like Nonabokra and Pokkali show a high level of tolerance towards salinity stress compared to IR64 variety. This differential response of tolerant varieties towards salinity stress may be a cumulative effect of genetic and epigenetic factors. In this study, we have compared the salinity-induced changes in chromatin modifications at the OsBZ8 locus in salt-tolerant Nonabokra and salt-sensitive IR64 rice varieties. Expression analysis indicates that the OsBZ8 gene is highly induced in Nonabokra plants even in the absence of salt stress, whereas in IR64, the expression significantly increases only during salt stress. Sequence analysis and nucleosomal arrangement within the region -2000 to +1000 of OsBZ8 gene show no difference between the two rice varieties. However, there was a considerable difference in histone modifications and DNA methylation at the locus between these varieties. In Nonabokra, the upstream region was hyperacetylated at H3K9 and H3K27, and this acetylation did not change during salt stress. However, in IR64, histone acetylation was observed only during salt stress. Moreover, the upstream region of OsBZ8 gene has highly dynamic nucleosome arrangement in Nonabokra, compared to IR64. Furthermore, loss of DNA methylation was observed at OsBZ8 locus in Nonabokra control plants along with low H3K27me3 and high H3K4me3. Control IR64 plants show high DNA methylation and enriched H3K27me3. Collectively these results indicate a significant difference in chromatin modifications between the rice varieties that regulates differential expression of OsBZ8 gene during salt stress.

Background: Cellular reprogramming in response to environmental stress involves alteration of gene expression, changes in the protein and metabolite profile for ensuring better stress management in plants. Similar to other plant species originating in tropical and subtropical areas, indica rice is highly sensitive to low temperature that adversely affects its growth and grain productivity. Substantial work has been done to understand cold induced changes in gene expression in rice plants. However, adequate information is not available for early gene expression, especially in indica variety. Therefore, a transcriptome profile was generated for cold shock treated seedlings of IR64 variety to identify early responsive genes. Results: The functional annotation of early DEGs shows enrichment of genes involved in altered membrane rigidity and electrolytic leakage, the onset of calcium signaling, ROS generation and activation of stress responsive transcription factors in IR64. Gene regulatory network suggests that cold shock induced Ca2+ signaling activates DREB/CBF pathway and other groups of transcription factors such as MYB, NAC and ZFP; for activating various coldresponsive genes. The analysis also indicates that cold induced signaling proteins like RLKs, RLCKs, CDPKs and MAPKK and ROS signaling proteins. Further, several late-embryogenesis-abundant (LEA), dehydrins and low temperature-induced-genes were upregulated under early cold shock condition, indicating the onset of waterdeficit conditions. Expression profiling in different high yielding cultivars shows high expression of cold-responsive genes in Heera and CB1 indica varieties. These varieties show low levels of cold induced ROS production, electrolytic leakage and high germination rate post-cold stress, compared to IR36 and IR64. Collectively, these results suggest that these varieties may have improved adaptability to cold stress.

No abstract

Background: Cellular reprogramming in response to environmental stress involves alteration of gene expression, changes in the protein and metabolite profile for ensuring better stress management in plants. Similar to other plant species originating in tropical and sub-tropical areas, indica rice is highly sensitive to low temperature that adversely affects its growth and grain productivity. Substantial work has been done to understand cold induced changes in gene expression in rice plants. However, adequate information is not available for early gene expression, especially in indica variety. Therefore, a transcriptome profile was generated for cold shock treated seedlings of IR64 variety to identify early responsive genes. Results: The functional annotation of early DEGs shows enrichment of genes involved in altered membrane rigidity and electrolytic leakage, the onset of calcium signaling, ROS generation and activation of stress responsive transcription factors in IR64. Gene regulatory network suggests that cold shock induced Ca2+ signaling activates DREB/CBF pathway and other groups of transcription factors such as MYB, NAC and ZFP; for activating various cold-responsive genes. The analysis also indicates that cold induced signaling proteins like RLKs, RLCKs, CDPKs and MAPKK and ROS signaling proteins. Further, several late-embryogenesis-abundant (LEA), dehydrins and low temperature-induced-genes were upregulated under early cold shock condition, indicating the onset of water-deficit conditions. Expression profiling in different high yielding cultivars shows high expression of cold-responsive genes in Heera and CB1 indica varieties. These varieties show low levels of cold induced ROS production, electrolytic leakage and high germination rate post-cold stress, compared to IR36 and IR64. Collectively, these results suggest that these varieties may have improved adaptability to cold stress.Conclusions: The results of this study provide insights about early responsive events in Oryza sativa L.ssp. indica cv IR64 in response to cold stress. Our data shows the onset of cold response is associated with upregulation of stress responsive TFs, hydrophilic proteins and signaling molecules, whereas, the genes coding for cellular biosynthetic enzymes, cell cycle control and growth-related TFs are downregulated. This study reports that the generation of ROS is integral to the early response to trigger the ROS mediated signaling events during later stages.