For example, the gene hrcC, which expresses the pore-forming outer membrane protein, is located downstream from hrpE and without the pore the external needle effector proteins remain in the cytoplasm or periplasm of the bacteria. This phenotype this website has been shown for P. syringae, where the mutant strain in the hrpE gene did not cause a hypersensitive response in plants of Nicotiana tabacum [33]. H. rubrisubalbicans hrcN and hrpE mutants did not elicit lesions on V. unguiculata leaves. Thus, our results point to the involvement

of the H. rubrisubalbicans T3SS in the development of disease symptoms in V. unguiculata leaves. Interestingly, the H. rubrisubalbicans hrcN and hrpE mutants were less proficient in endophytic colonization of rice and maize, indicating that the T3SS genes have a dual function depending on the host. In susceptible hosts T3SS expression by H. rubrisubalbicans leads to the development of disease whereas in symptomless hosts the T3SS is important to avoid the plant response allowing bacterial colonization.

Impairment of the T3SS system also produced opposing effects on Q-VD-Oph cost different plants inoculated with the symbiotic nodulating bacterium Rhizobium sp. NGR234 [58]. Some leguminous plants are more effectively nodulated by an rhcN (hrcN homolog) mutant strain than by the wild type, while others display the opposite behavior. Molecular analysis of this behavior lead to the characterization of effector proteins as being positive, negative or neutral depending on the effect of their removal [59]. Since H. rubrisubalbicans strains can stimulate growth of some DMXAA clinical trial plants [8] it remains to be determined if the T3SS of such strains can contribute to the beneficial effects. Conclusions Our results showed that

a mutation in the hrpE and hrcN genes lead to a bacterium uncapable to cause the mottled stripe disease in B-4362 sugarcane, indicating that the H. rubrisubalbicans T3SS is necessary for the development of the disease. A decrease in rice endophytic colonization was also observed with these mutants, suggesting that in symptomless plants the H. rubrisubalbicans T3SS is important for endophytic colonization. Methods Bacterial strains The bacterial strains used in this study are listed in Table 2. Table 2 Bacterial strains Strains why Genotype/phenotype Reference Herbaspirillum rubrisubalbicans M1 Wild type strain (BALDANI et al., 1996) Herbaspirillum rubrisubalbicans TSE M1 hrpE – EZ::Tn5TM < TET1>, TcR, KmR This work Herbaspirillum rubrisubalbicans TSN M1 hrcN – EZ::Tn5TM < TET1>, TcR This work Escherichia coli TOP10 F- mcrA Δ(mcrr-hsdRMS-mcrBC) φ80lacZΔM15 ΔlacZX74 doeR recA1 endA1 araΔ139 Δ(ara, leu) 7697 galU galK λ- rpsL nupG λ- INVITROGEN Media and growth conditions Escherichia coli was grown at 37°C in LB medium [60]. Strains of H. rubrisubalbicans were grown at 30°C in NFbHPN-malate [61].