Plays a critical role in the general process of plant cell elongation. Involved in the synthesis of campesterol, an early precursor of brassinolide. Required for the conversion of 24-methylenecholesterol to campesterol and for the conversion of isofucosterol to sitosterol. Necessary for both the isomerization and reduction of 24-methylenecholesterol. Regulates indirectly phytochrome-mediated light responses through the modulation of brassinosteroid biosynthesis. lathosterol + NADP(+) = 5alpha-cholesta-7,24-dien-3beta-ol + H(+) + NADPH Interacts with calmodulin. Dwarf and reduced fertility. Belongs to the DIMINUTO family.