Serine Palmitoyltransferase, a Key Enzyme for de Novo Synthesis of Sphingolipids, Is Essential for Male Gametophyte Development in Arabidopsis    

Abstract

Sphingolipids are important signaling molecules involved in various cellular activities. De novo sphingolipid synthesis is initiated by a rate-limiting enzyme, serine palmitoyltransferase (SPT), a heterodimer consisting of LONG-CHAIN BASE1 (LCB1) and LCB2 subunits. A mutation in the Arabidopsis thaliana LCB1 gene, lcb1-1, was found to cause embryo lethality. However, the underpinning molecular and cellular mechanisms remain largely unclear. Here, we report the identification of the fumonisin B 1 resistant11-2 (fbr11-2) mutant, an allele of lcb1-1. The fbr11-2 mutation, most likely an allele stronger than lcb1-1, was transmitted only through female gametophytes and caused the formation of abortive microspores. During the second pollen mitosis, fbr11-2 initiated apoptotic cell death in binucleated microspores characteristic of nuclear DNA fragmentation, followed by cytoplasm shrinkage and organelle degeneration at the trinucleated stage. In addition, a double mutant with T-DNA insertions in two homologous LCB2 genes showed a phenotype similar to fbr11-2. Consistent with these observations, the FBR11/LCB1 expression was confined in microspores during microgametogenesis. These results suggest that SPTmodulated programmed cell death plays an important role in the regulation of male gametophyte development.

ORM Expression Alters Sphingolipid Homeostasis and Differentially Affects Ceramide Synthase Activities

“…Tagged ORM1 and ORM2 colocalized with the ER marker mCherry-HDEL (Fig. 3,C and F), consistent with the known ER localization of AtLCB1, AtLCB2a/ 2b, and AtssSPTa/b (Chen et al, 2006;Dietrich et al, 2008;Teng et al, 2008;Kimberlin et al, 2013), but also were detected in other subcellular locations, including the cytosol (Fig. 3, A, C, D, and F).…”

“…SPT synthesizes LCBs, unique components of sphingolipids, by catalyzing a pyridoxal phosphate-dependent condensation of Ser and palmitoyl (16:0)-CoA in plants (Markham et al, 2013). Similar to other eukaryotes, the Arabidopsis (Arabidopsis thaliana) SPT is a heterodimer consisting of LCB1 and LCB2 subunits (Chen et al, 2006;Dietrich et al, 2008;Teng et al, 2008). Research to date has shown that SPT is regulated primarily by posttranslational mechanisms involving physical interactions with noncatalytic, membrane-associated proteins that confer positive and negative regulation of SPT activity (Han et al, 2009Breslow et al, 2010).…”

Brassinosteroids control male fertility by regulating the expression of key genes involved in Arabidopsis anther and pollen development

“…Although some male-sterile mutants can produce pollen, they show reduced pollen viability (13,38,39). To test pollen viability in the BR biosynthetic and signaling mutants, we stained pollen grains with Alexander's solution (40), and found that nearly 99% of pollen grains from wild-type and a weak BR-biosynthetic mutant, det2-1 were viable, but the viability of pollen grains from a severe BR-biosynthetic mutant, cpd, a severe BR-perception mutant, bri1-116, a severe BR-signaling mutant, bin2-1, and myriBKI1-YFP-OX (34), was decreased to 95, 90, 94, and 95%, respectively (Fig.…”

The Arabidopsis PARAQUAT RESISTANT2 gene encodes an S-nitrosoglutathione reductase that is a key regulator of cell death

“…In contrast to that of the lesion mimic mutants, these fbr mutants show an anti-apoptotic phenotype [9][10][11][12]. Whereas FBR6 and FBR12 encode a plant-specific transcription factor, AtSPL14, and a eukaryotic translation initiation factor 5A, respectively [10,12], FBR11 encodes a subunit of serine palmitoyltransferase that catalyzes the first rate-limiting reaction of sphingolipid de novo synthesis [11,13]. Although sphingolipid-regulated cell death has been attributed to ROS production [11,14], the molecular link between these two classes of signaling molecules remains unclear.…”