Is a Potential Susceptibility Factor by Regulating the ROS Burst Negatively in the Wheat- f. sp. Interaction.

Rac/Rop proteins play important roles in the regulation of cell growth and plant defense responses. However, the function of Rac/Rop proteins in wheat remains largely unknown. In this study, a small G protein gene, designated as , was characterized from wheat () in response to f. sp. () and was found to be highly homologous to the Rac proteins identified in other plant species. Transient expression analyses of the TaRac6-GFP fusion protein in leaves showed that TaRac6 was localized in the whole cell. Furthermore, transient expression of TaRac6 inhibited Bax-triggered plant cell death (PCD) in . Transcript accumulation of was increased at 24 h post-inoculation (hpi) in the compatible interaction between wheat and , while it was not induced in an incompatible interaction. More importantly, silencing of by virus induced gene silencing (VIGS) enhanced the resistance of wheat (Suwon 11) to (CYR31) by producing fewer uredinia. Histological observations revealed that the hypha growth of was markedly inhibited along with more HO generated in the -silenced leaves in response to . Moreover, transcript levels of were significantly down-regulated, while those of and were significantly up-regulated. These results suggest that functions as a potential susceptibility factor, which negatively regulate the reactive oxygen species (ROS) burst in the wheat- interaction.