• Xylanase Inhibitor Protein
• Amylase
• sugar sensing
• transcriptome
• coleoptile
• rice
• anoxia
• ERF
• alcohol dehydrogenase
• Heat Shock Protein
• Expansin
• P450

Rice, an essential food crop for billion of people, has the ability to cope with a wide range of environmental conditions and, in particular, with oxygen limitation.
While tolerance to submergence is linked with the ability of rice to transport oxygen from the aboveground organs to submerged hypoxic tissues (escape strategy), rice germination under anoxia (true resistance) is a consequence of a poorly understood metabolic adaptation.
A crucial point in anoxic rice germination is the successful use of storage compounds such as starch and free sugars. Alpha-Amylase is produced in rice seeds under anoxia, while it is not in anoxia-intolerant cereals like wheat, barley and oat.
Rice seeds germinated in complete absence of oxygen develop only coleoptiles, which are longer than the aerobic ones.
In order to deepen our knowledge on the process of anoxic rice germination, we took advantage of the recently completed rice genome sequencing (http://www.ricearray.org) to compare and investigate 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 the anaerobic carbohydrate metabolism, suggesting the up-regulation of the steps required to produce and metabolize pyruvate and its derivatives. Sugars appear to play a signalling role under anoxia, with several genes indirectly up-regulated by anoxia-driven sugar starvation. The analysis of the effects of anoxia on the expansin gene families revealed that EXPA7 and EXPB12 are likely to be involved in the rice coleoptile elongation under anoxia. Genes coding for Ethylene Response Factors (ERFs) and Heat Shock Proteins are among the genes that are modulated by anoxia in both rice and Arabidopsis. The identification of anoxia-induced ERFs is suggestive, since 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 energy-saving strategy in the regulation of gene expression.