Comprehensive Analysis of Subcellular Localization, Immune Function and Role in Bacterial wilt Disease Resistance of Linn. ROP Family Small GTPases.

ROPs (Rho-like GTPases from plants) belong to the Rho-GTPase subfamily and serve as molecular switches for regulating diverse cellular events, including morphogenesis and stress responses. However, the immune functions of ROPs in Linn. (tomato) is still largely unclear. The tomato genome contains nine genes encoding ROP-type small GTPase family proteins (namely ) that fall into five distinct groups as revealed by phylogenetic tree. We studied the subcellular localization and immune response induction of nine SlRops by using a transient overexpression system in Domin. Except for SlRop1 and SlRop3, which are solely localized at the plasma membrane, most of the remaining ROPs have additional nuclear and/or cytoplasmic distributions. We also revealed that the number of basic residues in the polybasic region of ROPs tends to be correlated with their membrane accumulation. Though nine SlRops are highly conserved at the RHO (Ras Homology) domains, only seven constitutively active forms of SlRops were able to trigger hypersensitive responses. Furthermore, we analyzed the tissue-specific expression patterns of nine and found that the expression levels of , and were generally high in different tissues. The expression levels of , and significantly decreased in tomato seedlings after infection with (E.F. Smith) Yabuuchi et al. (GMI1000); the others did not respond. Infection assays among nine ROPs showed that SlRop3 and SlRop4 might be positive regulators of tomato bacterial wilt disease resistance, whereas the rest of the ROPs may not contribute to defense. Our study provides systematic evidence of tomato Rho-related small GTPases for localization, immune response, and disease resistance.