Soybean sterol composition and utilization by Phytophthora sojae

The sterol fraction of Glycine max (soybean) was found to contain a mixture of 13 major sterols which differed dramatically in composition between see ds and shoots. Typical C4-desmethyl Delta (5)-sterols, including sitosterol , predominate the sterol mixture of shoots, whereas C4-methyl sterol interm ediates, cycloartenol and 24(28)-methylene cycloartanol, accumulate in seed s. The significance of modified sterol profile of shoot compared to seed wa s relevant to the physiology of Phytophthora sojae, a phytopathogen of soyb ean shown to be auxotrophic for sterol. Sterols native to the host plant co ntaining a C4-methyl group, such as cycloartenol, were not utilized by the fungus. Alternatively, all Delta (5)-sterols added to the culture media of P. sojae supported normal growth and promoted viable oospore production. Th e results demonstrate the importance of sterols in plant-fungal interaction s and offer the possibility of bioengineering the phytosterol pathway for r esistance to phytopathogens which scavenge specific sterols of the host pla nt to complete the life cycle. (C) 2001 Elsevier Science Ltd. All rights re served.