<jats:title>ABSTRACT</jats:title><jats:p><jats:italic>Claviceps purpurea</jats:italic>, the fungal pathogen that causes the cereal disease ergot, produces glycerides that contain high levels of ricinoleic acid [(<jats:italic>R</jats:italic>)-12-hydroxyoctadec-<jats:italic>cis</jats:italic>-9-enoic acid] in its sclerotia. Recently, a fatty acid hydroxylase (<jats:italic>C. purpurea</jats:italic>FAH [CpFAH]) involved in the biosynthesis of ricinoleic acid was identified from this fungus (D. Meesapyodsuk and X. Qiu, Plant Physiol.<jats:bold>147:</jats:bold>1325-1333, 2008). Here, we describe the cloning and biochemical characterization of a<jats:italic>C. purpurea</jats:italic>type II diacylglycerol acyltransferase (CpDGAT2) involved in the assembly of ricinoleic acid into triglycerides. The<jats:italic>CpDGAT2</jats:italic>gene was cloned by degenerate RT-PCR (reverse transcription-PCR). The expression of this gene restored the<jats:italic>in vivo</jats:italic>synthesis of triacylglycerol (TAG) in the quadruple mutant strain<jats:italic>Saccharomyces cerevisiae</jats:italic>H1246, in which all four TAG biosynthesis genes (<jats:italic>DGA1</jats:italic>,<jats:italic>LRO1</jats:italic>,<jats:italic>ARE1</jats:italic>, and<jats:italic>ARE2</jats:italic>) are disrupted.<jats:italic>In vitro</jats:italic>enzymatic assays using microsomal preparations from the transformed yeast strain indicated that CpDGAT2 prefers ricinoleic acid as an acyl donor over linoleic acid, oleic acid, or linolenic acid, and it prefers 1,2-dioleoyl-<jats:italic>sn</jats:italic>-glycerol over 1,2-dipalmitoyl-<jats:italic>sn</jats:italic>-glycerol as an acyl acceptor. The coexpression of CpFAH with CpDGAT2 in yeast resulted in an increased accumulation of ricinoleic acid compared to the coexpression of CpFAH with the native yeast DGAT2 (<jats:italic>S. cerevisiae</jats:italic>DGA1 [ScDGA1]) or the expression of CpFAH alone. Northern blot analysis indicated that<jats:italic>CpFAH</jats:italic>is expressed solely in sclerotium cells, with no transcripts of this gene being detected in mycelium or conidial cells. CpDGAT2 was more widely expressed among the cell types examined, although expression was low in conidiospores. The high expression of CpDGAT2 and CpFAH in sclerotium cells, where high levels of ricinoleate glycerides accumulate, provided further evidence supporting the roles of CpDGAT2 and CpFAH as key enzymes for the synthesis and assembly of ricinoleic acid in<jats:italic>C. purpurea.</jats:italic>