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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Oil Bodies and Oleosins in Physcomitrella Possess Characteristics Representative of Early Trends in Evolution^1,[W],[OA]

Center for Plant Cell Biology, Department of Botany and Plant Sciences, University of California, Riverside, California 92521 (C.-Y.H., C.-I.C., A.H.C.H.); and Institute of Plant and Microbial Biology, Academia Sinica, 11529, Taipei, Taiwan (C.-Y.H., Y.-C.L., Y.-I.C.H.)

Searches of sequenced genomes of diverse organisms revealed that the moss Physcomitrella patens is the most primitive organism possessing oleosin genes. Microscopy examination of Physcomitrella revealed that oil bodies (OBs) were abundant in the photosynthetic vegetative gametophyte and the reproductive spore. Chromatography illustrated the neutral lipids in OBs isolated from the gametophyte to be largely steryl esters and triacylglycerols, and SDS-PAGE showed the major proteins to be oleosins. Reverse transcription-PCR revealed the expression of all three oleosin genes to be tissue specific. This tissue specificity was greatly altered via alternative splicing, a control mechanism of oleosin gene expression unknown in higher plants. During the production of sex organs at the tips of gametophyte branches, the number of OBs in the top gametophyte tissue decreased concomitant with increases in the number of peroxisomes and level of transcripts encoding the glyoxylate cycle enzymes; thus, the OBs are food reserves for gluconeogenesis. In spores during germination, peroxisomes adjacent to OBs, along with transcripts encoding the glyoxylate cycle enzymes, appeared; thus, the spore OBs are food reserves for gluconeogenesis and equivalent to seed OBs. The one-cell-layer gametophyte could be observed easily with confocal microscopy for the subcellular OBs and other structures. Transient expression of various gene constructs transformed into gametophyte cells revealed that all OBs were linked to the endoplasmic reticulum (ER), that oleosins were synthesized in extended regions of the ER, and that two different oleosins were colocated in all OBs.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Anthony H.C. Huang (anthony.huang{at}ucr.edu).

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.109.138123

^* Corresponding author; e-mail anthony.huang{at}ucr.edu.

Received March 4, 2009; accepted April 29, 2009; published May 6, 2009.