Function AT14A Arabidopsis Proteins

AT14A is a membrane protein with unknown functions in Arabidopsis and has a small domain that has sequence similarities to integrins from animals. Integrin is a transmembrane linker of the extracellular matrix-plasma membrane-cytoskeleton continuum that is involved in cell adhesion and plays a bidirectional signal transducing role in animal cells. One of the primary differences between plant and animal cells is the difference of the outermost surface layer of cells. The plant cells have a cell wall composed predominantly of polysaccharides together with lesser amounts of wall proteins. There is also a cell wall-plasma membrane-cytokeleton continuum in plant cells.The basic mechanism of integrin function is very similar in animals and plants. So the sequence and structural similarity of AT14A to the integrins suggests that AT14A may be one of the members of the cell wall-plasma membrane-cytoskeleton continuum and carry out transmembrane signaling. The relationship between AT14A and composition of cell wall has been studied, and the results are as follows:1. The AT14A-GFP fusion gene was transformed into Arabidopsis seedlings and suspension cell lines by Agrobacterium-mediated method. And corresponding transgenic plants and suspension cell lines were constructed. The green fluorescence of GFP was observed in the cell membrane of epidermal cells and guard cells in which overexpression of AT14A-GFP fusion gene happened. It also proved the expression of AT14A-GFP fusion protein in the plasma membrane.2. Compositional analysis of cell wall polysaccharides isolated from the Arabidopsis seedlings of three different genotypes revealed substantial differences in cellulose, pectic substances and glucan contents. The cell wall of AT14A-overexpressed transformants had the highest cellulose content, which was significantly higher than wild type and atl4a mutant cell walls. The at14a mutant cell wall had higher pectic substances content than wild type and overexpressed transformants cell wall. And the glucans content of AT14A-overexpressed transformants and at14a mutant cell walls were significantly higher than wild type. The composition of polysaccharide in cell walls will change either where AT14A had been absented or overexpressed.3. An improved method of extraction and purification of cell wall proteins from Arabidopsis thaliana and corresponding proteome analysis were established. The compared analysis of the protein extraction efficiency of the new and old methods indicated that addition of C18column step as well as acetone precipitation process contributed to the purification of cell wall protein, the reduction of cell wall protein loss and improving the quality of electrophoresis and repetition rate.4. From the16unique protiens of the three genotype Arabidopsis cell walls by proteomic approaches,11proteins were determined. Among9proteins whose functions have been known, the xyloglucan endotransglucosylase/hydrolase7(XTH7) and encodes a GDP/GTP exchange factor for small G-proteins of the ADP ribosylation factor (RAF) class (EMB30) were related to the cell wall composition directly.5. The proteins interacted with AT14A were screened by yeast two-hybrid system from cDNA library of Arabidopsis. With AT14A-N-end as a bait, one screened protein named TSK-association proteinl (TSA1) might be related to cell wall.With AT14A-C-end as a bait, four proteins that take part in the cell wall metabolism or the reponse to stresses were screened. Among the four proteins, a-xylosidase is involved in the metabolic process of xylan and xyloglucan directly. These results suggested that there be a close relationship between the AT14A and the cell wall.Taken together, the function of AT14A is closely related to the cell wall composition and may be serve as a transmembrane linker between the cell wall and the cytoskeleton.