Raman Ramesh

Key message Colletotrichum falcatum- secreted proteins, Cf EPL1 and Cf PDIP1, trigger immune responses and confer broad-spectrum disease resistance in Nicotiana tabacum against bacterial diseases. Abstract Small secreted proteins (SSPs) play crucial roles in pathogenicity and host manipulation. C. falcatum, the causative agent of red rot in sugarcane, secretes numerous SSPs during its interaction with the host. In this study, three abundantly secreted SSPs of C. falcatum—CfEPL1 (eliciting plant response-like protein 1), CfPDIP1 (plant defence inducing protein 1), and CfBYS1 (Blastomyces yeast phase-specific protein 1) were transiently expressed in the model system, Nicotiana tabacum, to delineate their functional roles. Upon co-expression with green fluorescent protein (GFP), fluorescence signals of all three SSPs were predominant in the apoplastic spaces, consistent with the localisation predictions. Among the three SSPs, transient expression of CfEPL1 and CfPDIP1 induced a hypersensitivity response (HR), reactive oxygen species (ROS) production, and callose deposition in the infiltrated regions. However, transient expression of CfBYS1 triggered neither visible HR nor prominent upregulation of defence-related genes. Transcription profiling of defence-related genes in N. tabacum leaves infiltrated with CfEPL1 and CfPDIP1 indicated an upregulation of various genes associated with systemic acquired resistance (SAR), salicylic acid (SA), and jasmonic acid (JA) pathways. Inoculation of Pseudomonas syringae pv. tomato DC3000 (Pto) at the site of CfEPL1 and CfPDIP1 infiltration resulted in attenuated disease lesion development. Similarly, a reduction in bacterial wilt disease severity was observed, when the vacuum-infiltrated tobacco plants were challenged with Ralstonia solanacearum, which was substantiated by pathogen biomass quantification and SAR-associated marker expression profiling. Overall, this study demonstrated that the two SSPs, CfEPL1 and CfPDIP1, could confer broad-spectrum disease resistance in N. tabacum. Graphical Abstract The alternative text for this image may have been generated using AI.

Cultivation of solanaceous vegetables such as eggplant and tomato is severely affected by bacterial wilt in the coastal regions of India. The causal agent Ralstonia pseudosolanacearum is soilborne bacterium, highly diverse, and able to survive in soil for many years without a host. Five bacterial wilt resistant eggplant (Solanum melongena) rootstock lines were evaluated by challenge inoculation and were found to show different levels of wilt incidence. Grafts of eggplant made on two rootstocks (S0004 and Surya) recorded reduced incidence of bacterial wilt (10 to 40) during greenhouse evaluation while in nongrafted seedlings, the wilt incidence was 80 to 100. Field evaluation of eggplant grafts made on Solanum torvum (Turkey berry), S0004, and Surya reduced the incidence of bacterial wilt compared to nongrafted seedlings. The lowest wilt incidence (0 and 1540) was observed in the field evaluations where S. torvum was used as rootstock, while the nongrafted control recorded 93100 wilt. Tomato seedlings grafted on S. torvum, Surya, and S0004 recorded very low bacterial wilt incidence (0 to 15) under greenhouse evaluation while the nongrafted seedlings recorded 80 to 100 wilt. Reduced bacterial wilt incidence (23 to 40) was observed in grafts of polyhouse-grown tomato hybrid (GS-600) made on S. torvum while the nongrafted seedlings were severely affected (80 to 100) in evaluation trials conducted for two years. From this study, it is evident that grafting of susceptible eggplant and tomato on resistant rootstocks, viz., S. torvum and Surya, could be a promising strategy in bacterial wilt management.

Rhizome rot or soft rot disease is one of the major problems in banana (Musa spp.) cultivation, as it causes germination failure and death of early stage plants. A roving survey conducted during 20...

Ralstonia solanacearum is an important soil-borne plant pathogen which causes bacterial wilt in a large number of crops. Bacterial Type Six Secretion System (T6SS) is known to participate in pathogenesis, bacterial interaction and inter-bacterial competition. Contribution of T6SS in the virulence of R. solanacearum on eggplant (Solanum melongena L) is studied. In this study, five T6SS gene (ompA, vgrG3, hcp, tssH and tssM) mutants have been developed by insertional mutagenesis and the virulence of the mutants was evaluated on eggplant. In general, the T6SS mutants showed significant reduction of wilt on eggplant. R. solanacearum mutant of ompA gene significantly reduced the wilt from day five through day eight in petiole inoculation. In soil drench inoculation, R. solanacearum mutant of vgrG3 gene reduced the wilt on eggplant and was significantly different throughout the experimental period. Other mutants, viz., tssH, tssM and hcp, also reduced the wilt during the initial stages of disease development. This is the first report on the role of T6SS genes, ompA, vgrG3, hcp and tssH on virulence of R. solanacearum.

Ralstonia solanacearum is an important plant pathogen which infects a large number of agriculturally important crops. The Type Three Secretion System (T3SS) plays a major role in its pathogenicity by secreting type III effectors (T3Es) which overthrow the host defence mechanism. The secretion of T3Es is transcriptionally regulated by hrpB and its secretion is dependent on the pili formed by hrcV gene. In this study, two T3SS mutants of R. solanacearum strain Rs-09-161 viz. Rs-HrpB⁻ and Rs-HrcV⁻ were developed through insertional mutagenesis. The method of development of insertional mutant is quite simple and reliable. The plasmid integrates through homologous recombination and in vitro studies have proved that the integration was stable for several generations. The mutants are non-pathogenic on its highly susceptible hosts, brinjal and tomato inoculated by soil drench method and by petiole inoculation directly into the vascular system. Further it was observed that the colonisation ability of the mutants was also highly reduced in the susceptible host. These mutants will be useful in validating putative T3E through translocation studies.

Ralstonia solanacearum is a well-known phytopathogen causing bacterial wilt in a large number of agriculturally important crops. The pathogenicity of R. solanacearum is expressed due to the presence of various virulence factors and effector proteins. In this study, various virulence factors and type III effector proteins of R. solanacearum that are present in the strains Rs-09-161 and Rs-10-244 were identified through bioinformatics approach and compared with other reference strains. R. solanacearum strains, Rs-09-161 and Rs-10-244 belong to the phylotype I, biovar3, and are the only sequenced strains from India infecting solanaceous vegetables. Similarity matrix obtained by comparing the sequences of virulence genes of Rs-09-161 and Rs-10-244 with other reference strains indicated that Rs-09-161 and Rs-10-244 share more than 99% similarity between them and are closely related to GMI1000. The virulence factors in R. solanacearum appear to be highly conserved in the R. solanacearum species complex. Rs-09-161 has 72 type III effectors whereas Rs-10-244 has 77. Comparison of the complete genes of type III effectors of Rs-09-161, Rs-10-244 and GMI1000 revealed the presence of 60 common effectors within them. Further, Rs-09-161 has two unique effectors and Rs-10-244 has four unique effectors. Phylogenetic trees of RipA, RipG, RipH and RipS effector sequences resulted in the grouping of the isolates based on their phylotypes. Group 1 consists of strains that belong to phylotype I including Rs-09-161 and Rs-10-244. Phylotype III strain CMR15 forms a group closely associated with phylotype I. The strains belonging to phylotypes II and IV have separated to form two different groups.