| Heterotrimeric GTP-binding protein (G protein), a kind of protein in the living cells, plays important physiologic regulate functions. During the process of transmembrane signal transduction, G protein influences the signal transduction on the plasma membrane. G protein consists ofα,β, andγsubunits. Gαsubunit plays a leading role during the process of signal transduction, while the role of Gβγdimers is to anchor Gαon the cell membrane and adjust Gα's activity by combining with it or separating from it. In addition, Gβγdimers plays important roles on the intracellular localization, regulating receptor function, influencing the activities of phospholipase Cβ, receptor kinase, and adenylate cyclase. Small G protein families, including Rab, Ras, Rho, Arf, and Ran GTPase, are involved in many important cell physiological activities. Rab protein, the largest one of small G protein families, is a molecular switch in the vesicle transportation, and plays a role on different stages of the vesicle formation, transport, adhesion, anchoring, and integration.The typical compatible and incompatible interactions, which are consist of wheat leaf rust resistance near-isogenic lines TcLr1 and Puccinia triticina virulent strain 05-22-64 or avirulent strain05-8-63①, were constructed. To clarify G proteins'functions on wheat leaf rust resistance, the roles of Gαsubunit, Gβsubunit, and small G protein Rab2 were detected during interactions of wheat and P. triticina from different levels on disease resistance or gene expression. It will further reveal the molecular mechanism of wheat leaf rust resistance.(1) By real-time quantitative PCR technique, we detected the gene expressions of Gα, Gβsubunits in the compatible and incompatible interactions of wheat and P. triticina. The results showed that the avirulent strains can induce the gene expression of G protein. The gene expression ofβsubunit had a peak at 24 h after inoculation, andαsubunit gene expression reached the peak after 48 h. The gene expressions ofαsubunit andβsubunit have reached the lowest point at 0 h after inoculation. While, after inoculating the virulent strain,αsubunit andβsubunit gene expressions were inhibited. At 12 h after inoculation,αsubunit andβsubunit gene expressions reached the lowest point. The gene expressions ofα subunit andβsubunit had a peak at 24 h after inoculation. In both compatible and incompatible interactions of wheat and P. triticina,βsubunit gene expression was higher and earlier thanαsubunit.(2) Gene expression of small G protein Rab2 was checked by real-time quantitative PCR in the compatible and incompatible interactions of wheat and P. triticina. The results indicated that during the infection process of P. triticina, Rab2 gene mainly expressed rapidly in the early invasion, and reached a peak at 12 h after inoculation, and then gene expression decreased as time goes by. The avirulent strain can induce gene expression of the small G protein Rab2, while the virulent strain inhibite gene expression.(3)Using water as control, the activities of chitinase,β-1, 3–glucanase, and the rate changes of reactive oxygen ions production were detected in the compatible and incompatible interactions of wheat and P. triticina. Wheat leaves were smeared as one leaf with G protein inhibitor pertussis toxin PTX, and then inoculated with the avirulent strain after 24 h. All treatments were sampled at 0, 12, 16, 24, 48, 72, 96, 120, 144 h. In contrast with the inoculation by virulent or avirulent strains respectively, we found that G protein inhibitors distinctly decreased activities of defense enzymes induced by the avirulent strain. The inoculation treatment with the avirulent strain can induce the activities of chitinase andβ-1, 3 - glucanase increased, and can speed up the reactive oxygen ions produce.Gα, Gβsubunit of G protein, and the small G protein Rab2 play important roles in the resistance of wheat to P. triticina, and may be involved in the process of signal transduction. The avirulent strain enhanced the expression of the G protein gene, while the virulent strain inhibited gene expression. Different subunits of G protein display different priorities in the process of disease resistance signal transduction. Theβsubunit gene expression is earlier and higher thanαsubunit. In addition, G protein can increase the resistance to P. triticina through inducting the increase of defense enzymes'activities. |
