## 1 Introduction  
Briefly, 1-octen-3-ol is the source of a characteristic mushroom aroma first found in _Tricholoma matsutake_ and is known as mushroom alcohol [1]. It was subsequently discovered to be in a variety of mushrooms and molds [2; 3; 4], plants, animals, and their products [5; 6]. The main aromatic component of the button mushroom (_Agaricus bisporus_) is 1-octen-3-ol [7], which is synthesized largely in the mushroom's cap and gills [8], and in much higher amounts than in other edible mushrooms [9]. There is a very low olfactory threshold for 1-octen-3-ol [6], and thus, it is applied as a food additive authorized by the US Food and Drug Administration (ASP 1154, Regnum 172.515) [10]. In addition, 1-octen-3-ol also influences the growth, development, and behavior of fungi, plants, and insects ([PERSON], 2018; [PERSON], 2019) [11; 12; 13] as the signaling molecule oxylipin [14] and a quorum-sensing molecule [15]. In particular, 1-octen-3-ol is proposed to be a self-inhibitor for the primordium formation of the button mushroom [16; 17]. The 1-octen-3-ol produced by the natural oxidation of linoleic acid or chemical synthesization is a mixture of two enantiomers of (R)-(\(-\))-1-octen-3-ol and (S)-(+)-1-octen-3-ol in equal amounts [18], while (R)-(\(-\))-1-octen-3-ol is predominantly produced by biosynthesis, especially in button mushrooms (up to 99% of (R)-(\(-\))-1-octen-3-ol) [10]. (S)-(+)-1-octen-3-ol has a moldy, grassy aroma [19] and low biological activity [20]. Therefore, the application of the homogenates of button mushrooms to break down polyunsaturated fatty acids (PUFAs)such as linoleic acid for the production of 1-octen-3-ol has been commercialized [9; 21; 22]. However, the process conditions are very demanding, with the homogenization of the mushrooms occurring at 4 \({}^{\circ}\)C and enzyme reactions at 4-7.5 \({}^{\circ}\)C to avoid enzyme degradation by self-proteases. This is essentially due to the fact that the enzymes of _A. bisporus_ for the synthesis of 1-octen-3-ol remain obscure. Once the enzymes of _A. bisporus_ involved in the biosynthesis of 1-octen-3-ol are clearly identified, the enzymes can be exogenously expressed for large-scale applications. In addition, the biological functions of 1-octen-3-ol within the mushroom can be clarified. The enzymes that cleave linoleic acid to generate oxylipins in fungi include monooxygenases, dioxygenases, and hydroperoxide lyases [14; 23]. Monooxygenases introduce a single oxygen atom into the linoleic acid to mediate \(\omega\)-oxidation [14]. Lipoxygenases (LOXs) are nonheme-containing dioxygenases that introduce molecular oxygen into linoleic acid to generate hydroperoxides containing conjugated dienes. Heme-containing dioxygenases (DOXs) insert molecular oxygen into linoleic acid to form hydroperoxides without conjugated dienes [24]. Fatty acid hydroperoxide lyase (HPL) catalyzes the cleavage of C-C bonds in the hydroperoxides of PUFAs to form short-chain aldehydes and \(\omega\)-oxoacids [25]. The structure and function of fungal DOXs are quite diverse. Some DOXs contain only a fatty acid heme peroxidase/dioxygenase domain at the N-terminal, named DOX. Some DOXs are fusion enzymes containing a fatty acid heme peroxidase/dioxygenase domain at the N-terminus and a cytochrome P450 heme-thiolate domain at the C-terminus, cataloged as DOX-CYP. The type of DOX-CYP that has C-terminal CYP domains and linoleic did synthase activity is designated as DOX-LDS or LDS. The type of DOX-CYP that has C-terminal CYP domains and epoxy alcohol synthase activity is designated as DOX-EAS. The type of DOX-CYP that has C-terminal CYP domains and allene oxide synthase activity is designated as DOX-AOS. The fusion enzymes with no functional P450 heme-thiolate domains are designated as DOX-(CYP) [14; 23; 26]. Several oxo- and hydroxy acids were found to produce 1-octene-3-ol in a reaction system of mushroom homogenates of _A. campestris_ and linoleic acid. The _A.