NOVELTY - A genetically modified host cell comprising a 369 base pair sequence (SEQ ID NO: 2) or its fragment or variant capable of methylating a fatty acid, is new.    USE - The genetically modified host cell is useful for producing methylated fatty acids chosen from saturated fatty acid including acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, caprylic acid, nonanoic acid, capric acid, lauric acid, myristic acid, palmitic acid, heptadecanoic acid, stearic acid, arachidic acid, behenic acid or lignoceric acid, n-3 unsaturated fatty acid including alpha -linolenic acid, stearidonic acid, eicosapentaenoic acid or docosahexaenoic acid, n-6 unsaturated fatty acid including linoleic acid, gamma -linolenic acid, dihomo- gamma -linolenic acid or arachidonic acid, and n-9 unsaturated fatty acid chosen from oleic acid, elaidic acid, eicosenoic acid, erucic acid or nervonic acid, preferably caprylic acid, nonanoic acid, capric acid or palmitic acid, and biodiesel (claimed) or biofuel.    ADVANTAGE - The biodiesel is produced by cost-effective and environmentally-friendly process.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) method of cultivating or growing a genetically modified host cell, involves inoculating culture medium with one or more genetically modified host cells, and cultivating or growing the cells;    (2) method of producing methylated fatty acids, involves cultivating one or more genetically modified host cells in medium that allows methylation of a fatty acid;    (3) composition comprising one or more genetically modified host cells and medium;    (4) method of producing biodiesel, involves cultivating a genetically modified host cell in medium comprising crop oil, waste oil or animal fat, and methylating fatty acids in the medium; and    (5) transgenic plant, preferably an oil crop plant transformed with nucleic acid encoding PtJBMTm3 or its fragments capable of methylating fatty acids.