Working group session:
Functional Genomics
Presentation type:
poster
Authors:
Ting, Wei; fang, Li; yunlan, Zhai; zhifeng, Zeng; yingchai, Tang; chuang, Zhou; shue, Ye; ming, Luo
Presenter:
Ting, Wei; fang, Li; yunlan, Zhai; zhifeng, Zeng; yingchai, Tang; chuang, Zhou; shue, Ye
Correspondent:
ming, Luo
Abstract:
Phytosterol, as the precursor of bioactive brassinosteroids and a kind of content of cell membrane, plays an important role in plant growth and development. Sitosterol and campesterol are two major phytosterols in plant cell. Their content and the ratio of campesterol to sitosterol influenced the membrane fluidity and permeability, the membrane-associated metabolic processes, the activity of proteins within the membrane, Vesicle trafficking, and bioactivity BRs biosynthesis. Sterols become functional only after removal of the two methyl groups at C-4 site. In Animals and fungi, two C-4 demethylation is performed in one step. In the plant, however, is performed by two reactions separated by several steps. The biological significance of the phytosterol biosynthesis pathway in plants is largely unknown. Enzymology study showed each C-4 demethylation included three consecutive reaction performed by a C-4 demethylation complex which composed of a sterol methyl oxidase (SMO), a 3 beta steroid dehydrogenase/C-4 decarboxylase (3β HSD/D), and a 3-ketone reductase (SR). In plant, SMO1 and SMO2 mediated the first and the second demethylation reaction, respectively. To understand the role of two reactions in plant cells, we have cloned SMO1 and SMO2 genes from cotton fiber. There were two GhSMO1 genes in upland cotton and each protein contained 304 amino acid residues. Both GhSMO1-1 and GhSMO1-2 were membrane protein while four transmembrane domains were in GhSMO1-1 and three transmembrane domains were in GhSMO1-1. 89.5% identical amino acid shared by two proteins. Similarly, there were two GhSMO2 genes in upland cotton. The GhSMO2-1 and GhSMO2-2 contained 271 and 269 amino acid residues, respectively. Both proteins were soluble protein and there were 90.0% identical amino acid in two GhSMO2. The homology between GhSMO1-1 and GhSMO2-1 was 40.6% while the homology between GhSMO1-2 and GhSMO2-2 was 42.4%. These results suggested that the GhSMO mediated two demethylation was very different on sequence and the subcellular localization. The GhSMO1-1 and GhSMO1-2 expressed similarly in fibers and ovules. Following fiber and ovule growth, their expression levels increased gradually and reached to peak in 10 dpa, after that gradually decreased. However, there was not significant difference between various developmental stages of fiber and ovule. The GhSMO2-1 and GhSMO2-2 expressed preferentially in fiber cell. As the fiber grows, their expression levels increased drastically and reached to peak at rapid elongation stage of fiber (8-12 DPA). Furthermore, their expression levels elevated with ovule development in Xuzhou 142 wild type while extremely low level was detected and decreases gradually with ovule growth. These results suggested that the GhSMO1 might be a house-keeping gene and the first reaction was the basis for plant growth. The GhSMO2 and the second demethylation were closely related to the fiber cell elongation.