We also wonder what function s both FPPS

We also wonder what function(s) both FPPS1 and FPPS2 genes had in leaf. As some research indicated that the alpha-farnesene was also detected in ripe leaf of crabapple (Malus sp.) (Wu et al., 2012), one or both of them may be related to the synthesis of alpha-farnesene in leaf. To our knowledge, there is no other report concerning two FPPS genes and their expression comparison in apples and other fruit trees so far.
Conclusions A gene FPPS2 consisting of 11 introns and 12 exons was isolated from apples. Interestingly, although its each intron size was different from that of FPPS1 gene, its various exon sizes were the same as those of FPPS1 gene. It expressed in fruit and leaf; its expression level was obviously lower than that of FPPS1 gene in fruit which was stored at 4°C for 5weeks.
Conflict of interests
Acknowledgements This work was supported by the research foundation for PhD researcher in Shandong Academy of Agricultural Sciences (No. 2006YBS011) and an open research fund from National Laboratory of Plant Molecular Genetics, Institute of Plant Physiology & Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences. Thanks are given to Xiaoya Chen, Lingjian Wang and Changqing Yang, Institute of Plant Physiology & Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences for their help in the work and improving article.
Introduction There is an urgent need for antimalarials with novel mechanisms of action to circumvent resistance to frontline drugs. The biosynthesis of cellular isoprenoids is an essential process in Plasmodium parasites that cause malaria. A number of antimalarial compounds target iMDK receptor in isoprenoid biosynthetic pathways leading to parasite growth inhibition. First, Plasmodium parasites depend on the 7-enzyme prokaryotic 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway in its plastid organelle, the apicoplast, to produce isopentenyl pyrophosphate (IPP) and its isomer dimethyallyl pyrophosphate (DMAPP) (Jomaa et al., 1999). IPP and DMAPP are the C5 building blocks for all isoprenoids. The antibiotic fosmidomycin inhibits the MEP enzyme, Dxr/IspC, in both bacteria and Plasmodium parasites (Jomaa et al., 1999). Second, at least three isoprenoid synthases (PF3D7_1128400.1, PF3D7_0202700, PF3D7_0826400) catalyze the condensation of IPP and DMAPP into longer prenyl chains (Artz et al., 2011, Jordão et al., 2013, Tonhosolo et al., 2005). In particular, farnesyl pyrophosphate synthase (FPPS) and geranylgeranyl pyrophosphate synthase (GGPPS) are key branchpoint enzymes that synthesize C15 and C20 prenyl chains, respectively, for multiple downstream enzymes. In Plasmodium parasites, these reactions are catalyzed by a single bifunctional enzyme, the farnesyl/geranylgeranyl diphosphate synthase (Artz et al., 2011, Jordão et al., 2013). Nitrogen-containing bisphosphonates, blockbuster drugs that inhibit human FPPS, also inhibit the bifunctional Plasmodium FPPS/GGPPS (Ghosh et al., 2004, Jordão et al., 2011, Martin et al., 2001, No et al., 2012, Singh et al., 2010). Finally, prenyl chains are cyclized and/or conjugated to small-molecule and protein scaffolds by a variety of prenyltransferases to biosynthesize final isoprenoid products required for parasite growth and replication. Tetrahydroquinolines (THQs) have been shown to potently inhibit the Plasmodium protein farnesyltransferase (Eastman et al., 2005, Eastman et al., 2007, Nallan et al., 2005). Other inhibitors may interfere with isoprenoid biosynthesis indirectly by disrupting transporters that supply starting substrates or export products or blocking pathways that provide cofactors for isoprenoid biosynthetic enzymes. Importantly, fosmidomycin, bisphosphonates, and tetrahydroquinolines have all shown efficacy in mouse models of malaria infection, validating the key importance of isoprenoid biosynthesis as an antimalarial drug target (Jomaa et al., 1999, Nallan et al., 2005, No et al., 2012, Singh et al., 2010). Fosmidomycin is currently being tested in human clinical trials, while a THQ lead candidate was investigated in preclinical studies (Fernandes et al., 2015, Nallan et al., 2005). However, novel chemical scaffolds that disrupt isoprenoid biosynthetic pathways in Plasmodium remain desirable to overcome unfavorable drug properties of these known inhibitors. For example, bisphosphonates avidly bind bone mineral, and both fosmidomycin and THQs have short half-lives in vivo (Cremers et al., 2005, Sinigaglia et al., 2007, Tsuchiya et al., 1982, Van Voorhis et al., 2007).