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Title: Loss-of-function mutations and inducible RNA: suppression of Arabidopsis LCB2 genes reveal the critical role of sphingolipids in gametophytic and sporophytic cell viability

Author
item Dietrich, Charles
item GONGSHE, HAN - UNIV OF HEALTH SCIENCES
item CHEN, MING - DON DANFORTH PLT SCI CTR
item BERG, R. HOWARD - DON DANFORTH PLT SCI CTR
item DUNN, TERESA - UNIV OF HEALTH SCIENCES
item Cahoon, Edgar

Submitted to: Plant Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2007
Publication Date: 4/1/2008
Citation: Dietrich, C.R., Gongshe, H., Chen, M., Berg, R., Dunn, T.M., Cahoon, E.B. 2008. Loss-of-function mutations and inducible RNA: suppression of Arabidopsis LCB2 genes reveal the critical role of sphingolipids in gametophytic and sporophytic cell viability. Plant Journal. 54(2):284-298.

Interpretive Summary: The plasma membrane or outer membrane of plant cells plays important roles in growth and in the response of plants to environmental stresses such as drought and freezing. Sphingolipids are one of the major components of the plasma membrane whose contributions to the physiology of the plant cell have not been well-defined. In this study, sphingolipid synthesis was genetically shut off or attenuated in plant cells in order to gain a more precise view of the function of these molecules. Results from these studies demonstrated that sphingolipids are essential for pollen development and that complete or partial blockage of sphingolipid synthesis dramatically alters membrane structure and cell viability. This research provides useful information for biologists and plant breeders who are attempting to improve productivity and environmental stress tolerance in crops such as soybean. It is anticipated that this research will contribute basic information for the development of crops for US farmers that have improved yield.

Technical Abstract: Serine palmitoyltransferase (SPT) catalyzed the condensation of serine and palmitoyl-CoA and is the committed step in sphingolipid biosynthesis. Sphingolipids are essential components of all eukaryotic cells and have many diverse roles in plant development including structural roles as components of membranes and lipid rafts and signaling roles in guard cell closure and programmed cell death. SPT is a herterodimer consisting of the LCB1 and LCB2 subunits. Here we have characterized the two Arabidopsis genes that encode for the LCB2 subunit and for the first time describe a loss-of-function phenotype for a plant LCB2 mutant. We have shown that both LCB2 polypeptides can form heterodimers with the Arabidopsis LCB1 subunit of SPT by complementation of a yeast SPT auxotroph. Mutants in either LCB2 gene alone had no effect on the long-chain base composition of the plant but double mutants were found to be gametophytic lethal. Ultrastructure analysis reveals defects in vacuole and intine formation in the unicellular microspore. In addition, loss-of-function of LCB2 by induction of an RNAi expression cassette results in a double LCB2 knockout in sporophtyic tissue and causes a cell death phenotype that could be complemented by exogenous long-chain bases. These mutations provide new insights into the essential nature of sphingolipids and are unique tools for future experiments into the regulation of sphingolipid metabolism.