Arabidopsis 56-amino acid serine palmitoyltransferase-interacting proteins stimulate sphingolipid synthesis, are essential, and affect mycotoxin sensitivity.
Maintenance of sphingolipid homeostasis is critical for cell growth and programmed cell death (PCD). Serine palmitoyltransferase (SPT), composed of LCB1 and LCB2 subunits, catalyzes the primary regulatory point for sphingolipid synthesis. Small subunits of SPT (ssSPT) that strongly stimulate SPT activity have been identified in mammals, but the role of ssSPT in eukaryotic cells is unclear. Candidate Arabidopsis thaliana ssSPTs, ssSPTa and ssSPTb, were identified and characterized. Expression of these 56-amino acid polypeptides in a Saccharomyces cerevisiae SPT null mutant stimulated SPT activity from the Arabidopsis LCB1/LCB2 heterodimer by >100-fold through physical interaction with LCB1/LCB2. ssSPTa transcripts were more enriched in all organs and >400-fold more abundant in pollen than ssSPTb transcripts. Accordingly, homozygous ssSPTa T-DNA mutants were not recoverable, and 50% nonviable pollen was detected in heterozygous ssspta mutants. Pollen viability was recovered by expression of wild-type ssSPTa or ssSPTb under control of the ssSPTa promoter, indicating ssSPTa and ssSPTb functional redundancy. SPT activity and sensitivity to the PCD-inducing mycotoxin fumonisin B1 (FB1) were increased by ssSPTa overexpression. Conversely, SPT activity and FB1 sensitivity were reduced in ssSPTa RNA interference lines. These results demonstrate that ssSPTs are essential for male gametophytes, are important for FB1 sensitivity, and limit sphingolipid synthesis in planta.
Center for Plant Science Inovation and Department of Biochemistry, University of Nebraska-Lincoln, Lincoln, Nebraska 68588.
Athen N
AN
Kimberlin
Saurav
S
Majumder
Gongshe
G
Han
Ming
M
Chen
Rebecca E
RE
Cahoon
Julie M
JM
Stone
Teresa M
TM
Dunn
Edgar B
EB
Cahoon
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D016923:Cell Death / Q000187:drug effects; D004269:DNA, Bacterial; D037341:Fumonisins / Q000494:pharmacology; D008969:Molecular Sequence Data; D009154:Mutation; D009183:Mycotoxins / Q000494:pharmacology*; D010802:Phylogeny; D030821:Plants, Genetically Modified; D011058:Pollen / Q000235:genetics; D011401:Promoter Regions, Genetic; D012441:Saccharomyces cerevisiae / Q000235:genetics; D051102:Serine C-Palmitoyltransferase / Q000235:genetics / Q000378:metabolism*; D013107:Sphingolipids / Q000096:biosynthesis*; D013379:Substrate Specificity
D029681:Arabidopsis Proteins; D004269:DNA, Bacterial; D037341:Fumonisins; D009183:Mycotoxins; D013107:Sphingolipids; C036483:T-DNA; C056933:fumonisin B1; C518504:LCB1 protein, Arabidopsis; C530166:Lcb2 protein, Arabidopsis; D051102:Serine C-Palmitoyltransferase