Abstract
A transcriptomic approach has been used to identify genes predominantly expressed in maize (Zea mays) scutellum during maturation. One of the identified genes is oil body associated protein1 (obap1), which is transcribed during seed maturation predominantly in the scutellum, and its expression decreases rapidly after germination. Proteins similar to OBAP1 are present in all plants, including primitive plants and mosses, and in some fungi and bacteria. In plants, obap genes are divided in two subfamilies. Arabidopsis (Arabidopsis thaliana) genome contains five genes coding for OBAP proteins. Arabidopsis OBAP1a protein is accumulated during seed maturation and disappears after germination. Agroinfiltration of tobacco (Nicotiana benthamiana) epidermal leaf cells with fusions of OBAP1 to yellow fluorescent protein and immunogold labeling of embryo transmission electron microscopy sections showed that OBAP1 protein is mainly localized in the surface of the oil bodies. OBAP1 protein was detected in the oil body cellular fraction of Arabidopsis embryos. Deletion analyses demonstrate that the most hydrophilic part of the protein is responsible for the oil body localization, which suggests an indirect interaction of OBAP1 with other proteins in the oil body surface. An Arabidopsis mutant with a transfer DNA inserted in the second exon of the obap1a gene and an RNA interference line against the same gene showed a decrease in the germination rate, a decrease in seed oil content, and changes in fatty acid composition, and their embryos have few, big, and irregular oil bodies compared with the wild type. Taken together, our findings suggest that OBAP1 protein is involved in the stability of oil bodies.
Highlights
A transcriptomic approach has been used to identify genes predominantly expressed in maize (Zea mays) scutellum during maturation
Our results demonstrate that Oil Body Associated Protein1 (OBAP1) is necessary to maintain the structure of the oil bodies (OBs) and for seed germination in Arabidopsis (Arabidopsis thaliana)
These results were confirmed by immunolocalization experiments of OBAP1a in electron microscopy samples of mature rapeseed embryos
Summary
A transcriptomic approach has been used to identify genes predominantly expressed in maize (Zea mays) scutellum during maturation. One of the identified genes is oil body associated protein (obap1), which is transcribed during seed maturation predominantly in the scutellum, and its expression decreases rapidly after germination. Triacylglycerols (TAGs) in seeds accumulate in special cytoplasmatic organelles called oil bodies (OBs; Murphy, 2001), which consist in a hydrophobic central core of neutral lipids, such as TAGs, surrounded by a monolayer of amphipathic phospholipids, glycolipids, and/or sterols, with a series of proteins bound to the surface of the OB (Purkrtova et al, 2008). Caleosins are a second group of plant proteins associated with OBs that contain a hydrophobic core of about 30 amino acids and an E-F hand calciumbinding motif in its C-terminal end (Chen et al, 1999; Frandsen et al, 2001). Our results demonstrate that Oil Body Associated Protein (OBAP1) is necessary to maintain the structure of the OBs and for seed germination in Arabidopsis (Arabidopsis thaliana)
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