Heterotrimeric G Protein In Arabidopsis Suspension Cell Division And Elongation In The Role

In present study, the role of heterotrimeric G-protein (G protein) in cell division and elongation of Arabidopsis thaliana suspension cells was explored using Gβsubunit null mutant agb1-2 suspension cells, GPA1-overexpressed suspension cells, AGB1-overexpressed suspension cells. The major results are as follows:1. The suspension cultured cells of wildtype Columbia were treated with different concentrations of 2,4-D and NAA, and the cell division and elongation were analyzed. The results showed that 2μM of 2,4-D significantly promoted the cell division, and the expression of GPA1 and AGB1 was also increased. As compared with control (no 2,4-D treatment), the ratio of length to width of these cells were obviously lower than those of no auxin treatment. 2μM of NAA treatment had no obvious stimulation on cell division, but significantly promoted the cell elongation. No obvious differences in GPA1 expression were observed, while the expression of AGB1 was increased significantly under the treatment of NAA, as compared with control.2. GPA1 and AGB1 were cloned from Arabidopsis ecotype Col by RT-PCR and TOPO-cloning technology and then were fused with GFP coding sequence, respectively. The reconstructed plasmid was introduced into Arabidopsis Col suspension cell by Agrobacterium-mediated method. Expression of GPA1 and AGB1 driven by 35S promoter was analyzed by detection of GFP fluorescence. It was showed that GPA1 and AGB1 were mainly located in the plasma membrane.3. Under no auxin treatment condition, the mitosis index of AGB1-overexpressed suspension cells was significantly lower than that of Col suspension cells, while those of agb1-2 mutant and GPA1-overexpressed suspension cells were obviously higher than Col. 2,4-D treatment stimulated the expression of cell cyclin gene of AtCYCD4;1 of all genotypes investigated. However, the expression of AtCYCD4;1 of agb1-2 mutant was relatively high under the condition of no auxin treatment or NAA treatment.4. Under no auxin treatment, the length of AGB1-overexpressed cells was longer than that of Col, and most of agb1-2 mutant suspension cells became spherical in shape and its cell length was significantly smaller than that of Col. Exogenous NAA treatment significantly promoted cell elongation of agb1-2 and GPA1-overexpressed suspension cells. RT-PCR result showed that, the ABP1 gene related to cell elongation, was highly expressed in agb1-2 and GPA1-overexpressed suspension cells when treated with NAA.Based on the results above, it was suggested that: (1) GPA1 promotes cell division induced by 2,4-D. (2) AGB1 negatively regulated cell division, and promoted cell elongation induced by NAA.