Elucidation of a novel pathway for phytosterol biosynthesis using ¹⁴C radioisotope

Major crop plants have been facing on environmental disasters such as flooding and drought caused by the unpredicted change of weather. In this study, we would like to demonstrate that the anaerobic metabolism is involved in biosynthesis of isoprenoids in response to biotic and abiotic stresses in plants. ○ A key gene in an anaerobic metabolism, a pepper alcohol dehydrogenase, was cloned and sequenced. We examined the differential expression of the gene under various stresses. We confirmed that capsidiol is biosynthesized in response to fungal infection through the anaerobic metabolism, conferring carbon source to the isoprenoid pathway. ○ We examined the overexpression of ACS, HMGR1, HMGR2, SQS, CAS, and SMT2 in aerial tissues under oxygen-deficient condition, and CAS, SMT2 and HMGR2 in root tissues, meaning that low oxygen is correlated with a downstream pathway of phytosterol biosynthetic pathway as well as with PDH-bypass pathway. ○ We quantified the level of expression of the genes in PDH-bypass pathway using qRT-PCR assay. PDC1, ADH1, and ALDH2a are inducibly expressed up to 1,500-fold in shoot and to 80-fold (except PDC1 of 1,500-fold) in root. ○ Under normoxic condition, ethanol was accumulated in a basal level, but transition to the oxygen-deficient condition elicits ethanol accumulation in significantly high level ○ We confirmed that citric acid also contributed to the production of phytosterols in shoot and root tissues.