Deduced pathway of sterol biosynthesis in N. oceanica , comparison among plants, humans and yeasts, and sites of action of inhibitors. Enzyme nomenclature is that commonly used in Arabidopsis, because although many human and yeast enzymes have different names and abbreviations, they catalyze equivalent reactions to those of the Arabidopsis enzymes. An exception is Arabidopsis DWF1 (a dual isomerase-reductase), which is absent in Nannochloropsis; instead, this alga has a human-type DHCR24 (the yeast equivalent is ERG4). Full names and functions of enzymes are provided in Additional file 3: Table S1. Lanosterol synthase (LAS) is found in Arabidopsis but has a minor role. Enzyme abbreviations: DXS, 1-deoxy-D-xylulose 5-phosphate synthase; HMGR, hydroxy-methyl-glutaryl-CoA reductase; HMGS, hydroxy-methyl-glutaryl-CoA synthase; SQE, squalene epoxidase; CAS, cycloartenol synthase; LAS, lanosterol synthase; SMT, sterol methytransferase; SMO, sterol 4-methyl oxidase; CPI, cycloeucalenol cycloisomerase; CYP51, sterol 14-alpha demethylase; FK, sterol C-14 reductase; HYD, sterol C-8 isomerase; DWF7, delta7 sterol C-5 desaturase; DWF5, sterol C-7 reductase; DWF1, sterol C-24(28) isomerase-reductase; CYP710A, sterol C-22 desaturase; DHCR24, dihydrocholesterol reductase; ERG4, sterol delta 24(28) reductase. Abbreviations for metabolites: MEP, methylerythritol phosphate; IPP, isopentenyl pyrophosphate; MVA, mevalonic acid. Abbreviations for inhibitors: CLO, clomazone; TBF, terbinafine; 25-AZA, 25-azalanosterol; TDM, tridemorph; TEB, tebuconazole.