Non-heme iron oxygenase involved in sterols biosynthesis by catalyzing the removal of the second methyl group at the C-4 position (PubMed:11707264). 24-ethylidenelophenol and 24-ethyllophenol are the preferred substrates (PubMed:11707264). Together with SMO2-1, required during embryogenesis, probably by maintaining sterols and auxin homeostasis (PubMed:27006488). 4,4-dimethyl-5alpha-cholest-7-en-3beta-ol + 6 Fe(II)-[cytochrome b5] + 5 H(+) + 3 O2 = 4alpha-carboxy-4beta-methyl-5alpha-cholest-7-ene-3beta-ol + 6 Fe(III)-[cytochrome b5] + 4 H2O 24-methylidenelophenol + 6 Fe(II)-[cytochrome b5] + 5 H(+) + 3 O2 = 4alpha-carboxy-ergosta-7,24(24(1))-dien-3beta-ol + 6 Fe(III)-[cytochrome b5] + 4 H2O Expressed in shoots, roots, siliques and flowers, and, slightly, in developing seeds. In shoots, restricted to the apical meristem (SAM) (PubMed:27006488). In roots, detected only in adventitious root primordia, lateral root primordia, and the root tip meristem (PubMed:27006488). In flowers, expressed in vascular tissues of sepals and petals as well as in stamen filaments and pollen (PubMed:27006488). In young siliques, confined to the style and silique funiculus (PubMed:27006488). In mature siliques, restricted to the abscission zone (PubMed:27006488). During embroygenesis, first expressed at very low levels in seeds at the early developmental stages; accumulates slightly in the late stages (PubMed:27006488). The histidine box domains may contain the active site and/or be involved in metal ion binding. No obvious phenotype (PubMed:27006488). The smo2-1 smo2-2 double mutant accumulates the 4alpha-methylsterols 24-ethylidene lophenol and 24-ethyl lophenol, and is embryonic lethal, arrested in early stages with an altered endosperm development, probably due to disturbed auxin flux and responses (PubMed:27006488). Requires a membrane-bound cytochrome b5 as an obligatory electron carrier from NAD(P)H to SMO. Belongs to the sterol desaturase family.