## 1 Introduction  
_Poria cocos_ (_P. cocos_) has been used as traditional medication for several thousand years in East Asia. The predominant triterpenoids in _P. cocos_ are pachymic acid and eburicoic acid. Previous studies have shown that triterpenoids separated from this fungus had a number of important pharmacological activities. Pachymic acid and dehydrotumulosic acid isolated from _P. cocos_ actively inhibited phospholipase A2 from snake venom [1]. [PERSON] et al (1995) [2] demonstrated that pachymic acid extracted from _P. cocos_ with a methylene group at C-24 exhibited antiemetic activity in frogs. Six lanostane-type triterpene acids isolated from _P. cocos_ showed cytotoxic activity against some human cancer cells [3,4]. However, despite the potential medical importance, little is known about the molecular biology of triterpenoid biosynthesis in _P. cocos_.  
Triterpenoids are synthesized via the isoprenoid pathway. The isoprenoid pathway constitutes the most diverse and widespread metabolic pathway of all prokaryotes and eukaryotes, resulting in the biosynthesis of a large number of primary as well as secondary metabolites. Isoprenoids are derived from common C\({}_{5}\) building blocks namely IPP and its isomer dimethylallyl diphosphate (DMAPP). IPP and DMAPP are synthesized via two independent and non-homologous pathways, the MVA (mevalonate) and MEP (2-C-methyl-D-erythritol 4-phosphate) pathways [5,6]. In plants and algae, isoprenoids are formed via both the MVA and MEP pathways [7]. In fungi, however, isoprenoids are synthesized through the classical MVA pathway. Different isoprenoids in fungi share all the early intermediates, up to FPP through the MVA pathway, which is catalyzed by acetoacetyl-CoA thiolase (AACT), 3-hydroxy-3-methylglutaryl-CoA synthase (HMGS), HMG-CoA reductase (HMGR), MVA kinase (MVK), phosphor mevalonate kinase (PMK), MVA-5-diphosphate decarboxylase (PMD), isopentenyl diphosphate isomerase (IDI) and farnesyl diphosphate synthase (FPS) (Figure 1) [8,9]. As shown in Figure 1, FPS is a key enzyme in terpenios biosynthesis, which catalyzes the consecutive condensations of dimethylallyl diphosphate (DMAPP) or GPP with IPP to produce FPP [10]. FPP is located at the first multiple branch point in the isoprenoid biosynthetic pathway for several terpenoids, like triterpenes, carotenoids, gibberellins and sterols [11].  
Upon until now, the complementary DNA (cDNA) or genomic DNA encoding FPS have been cloned and characterized from yeast, fungi, higher plants and human [10, 11, 12]. These studies have demonstrated that the FPS gene (_fps_) size varies from 1.2 to 2.1 kb. In plants, _fps_ belongs to a small multigenic family that encodes at least two different isoforms. _Arabidopsis thaliana_ contains two _fps_ genes, which encode three FPS isoforms [13]. Three FPS isoforms have also been discovered in both maize and _Artemisia tridentate_[14,15]. In human, only a single _fps_ encodes for FPS. Due to the alternative splicing in the first exon of human _fps,_ multiple splice variants are generated which encode two FPS isoforms: a shorter cytoplasmic/peroxisomal form, and a longer isoform which is a mitochondrial targeting peptide [16].  
So far, there are no reports about gene cloning and characterization of _fps_ from _P. cocos_. For a better understanding of the role of FPS in triterpenoids biosynthesis in _P. cocos_, we firstly needed to know the _fps_ and its expression profile in _P. cocos_; thus, we here describe the cloning and characterization of _fps_ from _P. cocos_. Further, the expression profile of _P. cocos_ FPS gene (_Pc-fps_), and content of total triterpenoids at different stages of development and methyl jasmonate treatments in _P. cocos_ were also investigated. Our results should be helpful for further study of its structure and expression, and facilitate the investigation of the role of FPS in the control of triterpenoids biosynthesis in _P. cocos_.