Sphingolipid Long-Chain Base Hydroxylation Is Important for Growth and Regulation of Sphingolipid Content and Composition inArabidopsis 

Abstract

Sphingolipids are structural components of endomembranes and function through their metabolites as bioactive regulators of cellular processes such as programmed cell death. A characteristic feature of plant sphingolipids is their high content of trihydroxy long-chain bases (LCBs) that are produced by the LCB C-4 hydroxylase. To determine the functional significance of trihydroxy LCBs in plants, T-DNA double mutants and RNA interference suppression lines were generated for the two Arabidopsis thaliana LCB C-4 hydroxylase genes Sphingoid Base Hydroxylase1 (SBH1) and SBH2. These plants displayed reductions in growth that were dependent on the content of trihydroxy LCBs in sphingolipids. Double sbh1 sbh2 mutants, which completely lacked trihydroxy LCBs, were severely dwarfed, did not progress from vegetative to reproductive growth, and had enhanced expression of programmed cell death associated-genes. Furthermore, the total content of sphingolipids on a dry weight basis increased as the relative amounts of trihydroxy LCBs decreased. In trihydroxy LCB-null mutants, sphingolipid content was ;2.5-fold higher than that in wild-type plants. Increases in sphingolipid content resulted from the accumulation of molecular species with C16 fatty acids rather than with very-long-chain fatty acids, which are more commonly enriched in plant sphingolipids, and were accompanied by decreases in amounts of C16-containing species of chloroplast lipids. Overall, these results indicate that trihydroxy LCB synthesis plays a central role in maintaining growth and mediating the total content and fatty acid composition of sphingolipids in plants.

Functional Characterization of a Higher Plant Sphingolipid Δ4-Desaturase: Defining the Role of Sphingosine and Sphingosine-1-Phosphate in Arabidopsis

“…Such data are starting to emerge regarding the role of phytosphingosine (Coursol et al, 2005;Shi et al, 2007;Chen et al, 2008) and also D8-unsaturated LCBs (Ryan et al, 2007). The significance of sphingolipids and their phosphorylated metabolites is still an evolving story in many eukaryotic systems, and it is hoped that studies such as this can contribute to the development of more precise models for their form and function in different organisms.…”

“…In that respect, it is interesting that Coursol et al (2005) reported a different LCB-1-P, phytosphingosine-1-P (t18:0-1-P), as being involved in Arabidopsis guard cell closure. Very recently, Chen et al (2008) demonstrated a crucial role for these C4-hydroxylated LCBs in Arabidopsis growth and development.…”

Isolation and characterization of Arabidopsis mutants with enhanced tolerance to oxidative stress

“…Sphingolipids are essential regulators not only of cell death, but also of development in both animal and plant cells (Teufel et al 2009;Chen et al 2008). This notion is supported by the various developmental defects in mutants with compromised very long-chain fatty acids that are components of sphingolipids and in mutants with impaired hydroxylation of long-chain bases (Bach et al 2008;Zheng et al 2005;Chen et al 2008). It could be that all mutants, being in loh2 background that lacks certain complex sphingolipids, are unable to proceed into mature plants when AAL toxin is present.…”

Highlights of recent progress in plant lipid research

“…In the plenary talk of this session (E. Cahoon, O44), it was reported that complete elimination of sphingolipid synthesis results in loss of Golgi bodies and aberrant ER morphology in pollen, leading to male gametophytic lethality [26]. In addition, complete or partial reductions in sphingolipid long-chain base (LCB) C-4 hydroxylation in Arabidopsis were shown to result in increases in total sphingolipid content due to the accumulation of sphingolipids with C16 species (E. Cahoon, O44) [27]. This structural modification was also shown to be important for growth of Arabidopsis (E. Cahoon, O44) and reproductive potential of rice (T. Imamura, P100) [28].…”