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J. Biol. Chem., Vol. 282, Issue 38, 28195-28206, September 21, 2007

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Arabidopsis Mutants Lacking Long Chain Base Phosphate Lyase Are Fumonisin-sensitive and Accumulate Trihydroxy-18:1 Long Chain Base Phosphate^*

Yoseph Tsegaye, Christopher G. Richardson, Janis E. Bravo, Brendan J. Mulcahy, Daniel V. Lynch¹, Jonathan E. Markham^¶, Jan G. Jaworski^¶, Ming Chen^¶, Edgar B. Cahoon^¶, and Teresa M. Dunn²

From the Department of Biochemistry and Molecular Biology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20184, the Department of Biology, Williams College, Williamstown, Massachusetts 01267, and ^¶Donald Danforth Plant Science Center, St. Louis, Missouri 63132

The sphingoid long chain bases (LCBs) and their phosphorylated derivatives (LCB-Ps) are important signaling molecules in eukaryotic organisms. The cellular levels of LCB-Ps are tightly controlled by the coordinated action of the LCB kinase activity responsible for their synthesis and the LCB-P phosphatase and lyase activities responsible for their catabolism. Although recent studies have implicated LCB-Ps as regulatory molecules in plants, in comparison with yeast and mammals, much less is known about their metabolism and function in plants. To investigate the functions of LCB-Ps in plants, we have undertaken the identification and characterization of Arabidopsis genes that encode the enzymes of LCB-P metabolism. In this study the Arabidopsis At1g27980 gene was shown to encode the only detectable LCB-P lyase activity in Arabidopsis. The LCB-P lyase activity was characterized, and mutant plant lines lacking the lyase were generated and analyzed. Whereas in other organisms loss of LCB-P lyase activity is associated with accumulation of high levels of LCB/LCB-Ps and developmental abnormalities, the sphingolipid profiles of the mutant plants were remarkably similar to those of wild-type plants, and no developmental abnormalities were observed. Thus, these studies indicate that the lyase plays a minor role in maintenance of sphingolipid metabolism during normal plant development and growth. However, a clear role for the lyase was revealed upon perturbation of sphingolipid synthesis by treatment with the inhibitor of ceramide synthase, fumonisin B₁.

Received for publication, June 20, 2007 , and in revised form, July 16, 2007.

^* This work was supported in part by National Science Foundation 2010 Program Collaborative Grants MCB-0312864 (to D. V. L.), MCB-0312559 (to J. G. J. and E. B. C.), and MCB-0313466 (to T. M. D.) and by National Science Foundation Postdoctoral Fellowship DBI-0511935 (to Y. T.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement"in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Supported by the Howard Hughes Medical Institute program for support of undergraduates at Williams College.

² To whom correspondence should be addressed: Dept. of Biochemistry and Molecular Biology, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Rd., Bethesda, MD 20184. Tel.: 301-295-3592; Fax: 301-295-3512; E-mail: tdunn{at}usuhs.mil.

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