Oil bodies and oleosins in Physcomitrella possess characteristics representative of early trends in evolution.
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.
Huang
Chien-Yu
CY
Center for Plant Cell Biology, Department of Botany, University of California, Riverside, California 92521, USA.
Chung
Chun-I
CI
Lin
Yao-Cheng
YC
Hsing
Yue-Ie Caroline
YI
Huang
Anthony H C
AH
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D005075:Biological Evolution; D019068:Bryopsida / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure*; D002845:Chromatography; D022083:Cytoplasmic Structures / Q000737:chemistry* / Q000648:ultrastructure; D004721:Endoplasmic Reticulum / Q000378:metabolism; D020676:Glyoxysomes / Q000378:metabolism; D008969:Molecular Sequence Data; D010788:Photosynthesis; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D013170:Spores / Q000378:metabolism / Q000648:ultrastructure
D010940:Plant Proteins