Transcript profiling of the anoxic rice coleoptile

Rice (Oryza sativa) seeds can germinate in the complete absence of oxygen. Under anoxia, the rice coleoptile elongates, reaching a length greater than that of the aerobic one. In this article, we compared and investigated the transcriptome of rice coleoptiles grown under aerobic and anaerobic conditions. The results allow drawing a detailed picture of the modulation of the transcripts involved in anaerobic carbohydrate metabolism, suggesting up-regulation of the steps required to produce and metabolize pyruvate and its derivatives. Sugars appear to play a signaling role under anoxia, with several genes indirectly up-regulated by anoxia-driven sugar starvation. Analysis of the effects of anoxia on the expansin gene families revealed that EXPA7 and EXPB12 are likely to be involved in rice coleoptile elongation under anoxia. Genes coding for ethylene response factors and heat shock proteins are among the genes modulated by anoxia in both rice and Arabidopsis (Arabidopsis thaliana). Identification of anoxia-induced ethylene response factors is suggestive because genes belonging to this gene family play a crucial role in rice tolerance to submergence, a process closely related to, but independent from, the ability to germinate under anoxia. Genes coding for some enzymes requiring oxygen for their activity are dramatically down-regulated under anoxia, suggesting the existence of an energysaving strategy in the regulation of gene expression.