Suppressing Farnesyl Diphosphate Synthase Alters Chloroplast Development and Triggers Sterol-Dependent Induction of Jasmonate- and Fe-Related Responses

Abstract

Farnesyl diphosphate synthase (FPS) catalyzes the synthesis of farnesyl diphosphate from isopentenyl diphosphate and dimethylallyl diphosphate. Arabidopsis (Arabidopsis thaliana) contains two genes (FPS1 and FPS2) encoding FPS. Single fps1 and fps2 knockout mutants are phenotypically indistinguishable from wild-type plants, while fps1/fps2 double mutants are embryo lethal. To assess the effect of FPS down-regulation at postembryonic developmental stages, we generated Arabidopsis conditional knockdown mutants expressing artificial microRNAs devised to simultaneously silence both FPS genes. Induction of silencing from germination rapidly caused chlorosis and a strong developmental phenotype that led to seedling lethality. However, silencing of FPS after seed germination resulted in a slight developmental delay only, although leaves and cotyledons continued to show chlorosis and altered chloroplasts. Metabolomic analyses also revealed drastic changes in the profile of sterols, ubiquinones, and plastidial isoprenoids. RNA sequencing and reverse transcription-quantitative polymerase chain reaction transcriptomic analysis showed that a reduction in FPS activity levels triggers the misregulation of genes involved in biotic and abiotic stress responses, the most prominent one being the rapid induction of a set of genes related to the jasmonic acid pathway. Down-regulation of FPS also triggered an iron-deficiency transcriptional response that is consistent with the irondeficient phenotype observed in FPS-silenced plants. The specific inhibition of the sterol biosynthesis pathway by chemical and genetic blockage mimicked these transcriptional responses, indicating that sterol depletion is the primary cause of the observed alterations. Our results highlight the importance of sterol homeostasis for normal chloroplast development and function and reveal important clues about how isoprenoid and sterol metabolism is integrated within plant physiology and development.Isoprenoids are the largest class of all known natural products in living organisms, with tens of thousands of different compounds. In plants, isoprenoids perform essential biological functions, including maintenance of proper membrane structure and function (sterols), electron transport (ubiquinones and plastoquinones), posttranslational protein modification (dolichols serving as glycosylation cofactors and prenyl groups), photosynthesis (chlorophylls and carotenoids), and regulation of growth and development (abscisic acid, brassinosteroids, cytokinins, and GAs [Croteau et al., 2000] and strigolactones [Al-Babili and Bouwmeester, 2015]). A large number of isoprenoids also play prominent roles as mediators of interactions between plants and their environment, including a variety of defense responses against biotic and abiotic stresses (Tholl and Lee, 2011). In fact, there is hardly any aspect of plant growth, development, and reproduction not relying on isoprenoids or isoprenoid-derived compounds. In addition, many plant isoprenoids are of great economic importan...

Improved fruit α‐tocopherol, carotenoid, squalene and phytosterol contents through manipulation of Brassica juncea 3‐HYDROXY‐3‐METHYLGLUTARYL‐COA SYNTHASE1 in transgenic tomato

“…SlFPS1 has been proposed to play an important role in early fruit development as well as cell division and elongation (Gaffe et al ., ). Simultaneous silencing of both FPS in Arabidopsis reduced sterol content and retarded seedling growth (Manzano et al ., ). While NtFPPS expression was slightly elevated in tobacco seedlings (Liao et al ., ), SlFPS1 expression in tomato OE‐wtBjHMGS1 seedlings remained unchanged and was up‐regulated in OE‐S359A (Figure ).…”

Functional Gene Network of Prenyltransferases in Arabidopsis thaliana

“…C-C double bonds in prenyl-PP can be either in trans or cis conformation depending on the PT-trans-PTs form trans isomers, and cis-PTs form cis-isomers. Considering the length of the produced carbon backbone, trans-PTs can be classified as short-chain PTs (C 10-25 ), medium-chain PTs (C [30][31][32][33][34][35], and long-chain PTs (C 40-50 ) [7]. Members of the short-chain ones are in ascending order C 10 geranyl diphosphate synthase (GPPS), C 15 farnesyl diphosphate synthase (FPPS), C 20 geranylgeranyl diphosphate synthase (GGPPS), and C 25 geranylfarnesyl diphosphate synthase (GFPPS) ( Table 1).…”

“…Last, but not least, FPP plays a very important role in protein prenylation and hence in cell signaling [26]. In A. thaliana, two FPPS genes were identified and characterized-FPPS1 (At5g47770) with two protein variants and FPPS2 (At4g17190) [25,[27][28][29][30][31][32]. The longer-variant FPPS1L is targeted to mitochondria, the shorter FPPS1S, together with the FPPS2, is localized to the cytosol.…”

“…The longer-variant FPPS1L is targeted to mitochondria, the shorter FPPS1S, together with the FPPS2, is localized to the cytosol. Research on this topic demonstrated that FPPS genes are redundant, thus one copy of the gene is enough to keep plants viable with only small changes in metabolite content [25,[30][31][32][33]. On the other hand, total loss of FPPS activity is lethal due to severely impaired embryo development [31].…”

The use of mutants and inhibitors to study sterol biosynthesis in plants

“…These condensation reactions are catalyzed by farnesyl pyrophosphate synthase (FPPS) (Kulkarni et al , 2013). In the plastidial MEP pathway, on the other hand, FPP is synthesized in two steps, in which IPP and DMAPP are first converted to GPP by GPPS followed by the formation of FPP from GPP and IPP by a plastidial FPPS (Manzano et al , 2016). In the cytosol, FPP can either enter the sesquiterpene biosynthesis pathway, or be further converted to squalene, a C-30 molecule which is a condensation of two FPP units catalyzed by squalene synthase (SQS) (Tansey and Shechter, 2001).…”