Abstract:

The differential expression of the key genes controlling isoprenoid metabolism in allelopathic and weak allelopathic rice accessions was investigated under two nitrogen supply levels using fluorescence quantitative polymerase chain reaction（FQ-PCR）. The results indicated that 12 detected key enzyme genes were mediated by lower nitrogen level. Of the twelve genes, six were up-regulated, and the others were down-regulated in allelopathic rice accession. In weak allelopathic rice Lemont, seven were up-regulated and five down-regulated. Of 12 tested genes, six up-regulated genes and five down-regulated genes detected in allelopathic rice PI312777 were founded in weak allelopathic rice Lemont. In other words, 11 out of 12 key genes involved in isoprenoid metabolic pathway in the two rice accessions had the same gene expression patterns under low nitrogen condition compared with the controls, suggesting that the related genes involved in isoprenoid metabolic pathway possessed the same or the similar ecological behavior in response to the changes of nitrogen supplies in the molecular scale. The further analysis showed that lower nitrogen supplies led to significantly declined expression of the key genes related to monoterpene, sesquiterpene, diterpene and triterpene. In conclusion, the increase of allelopathic potential induced by nutrient stress is not responsible for the variation of the terpenoid metabolism. It was also discussed that the relationships possibly existed among terpenoid synthesis decrease, hormone synthesis reduction and the plant growth inhibition, which in turn resulted in to a great extent, increased expression of the three genes encoding 3-hydroxy-3-methylglutaryl-CoA synthase, 3-hydroxy-3-methylglutaryl-CoA reductase and mevalonate kinase in the branch of mevalonate metabolism to sustain essential level of hormone for rice growth under nutrient stress condition.

Key words: Rice (Oryza Sativa L.), isoprenoids metabolic pathway, FQ-PCR, nitrogen stress