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Suppressing Farnesyl diphosphate synthase alters chloroplast development and triggers sterol-dependent induction of JA and Fe-related responses

Manzano, D., Andrade, P., Caudepon, D. et al.

Farnesyl diphosphate synthase (FPS) catalyzes the synthesis of farnesyl diphosphate (FPP) from isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). 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 post-embryonic developmental stages, we generated Arabidopsis conditional knockdown mutants expressing amiRNAs 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, though leaves and cotyledons continued to show chlorosis and altered chloroplasts. Metabolomic analyses revealed also drastic changes in the profile of sterols, ubiquinones and plastidial isoprenoids. RNA-seq and RT-qPCR transcriptomic analysis showed that a reduction in FPS activity levels triggers 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 (JA) pathway. Down-regulation of FPS also triggered a Fe-deficiency transcriptional response that is consistent with the Fe-deficient 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.

Citation

Manzano, D., Andrade, P., Caudepon, D. et al. "Suppressing Farnesyl diphosphate synthase alters chloroplast development and triggers sterol-dependent induction of JA and Fe-related responses" Plant Physiology (2016): 16.​00431