| Pseudomonas syringae pv. tomato strain DC3000 (Pst DC3000) delivers the virulence effector proteins into the host cells using the conserved type III secretion system (TTSS) and causes bacterial speck disease. Type III effectors modulate the physiology of the plants in susceptible hosts to sustain the growth of the pathogen. The type III independent virulence factor COR is similar to jasmonic acid in plants and contributes to virulence. The induction of RAP2.6-LUC reporter gene is closely associated with the bacterial virulence and its induction is largely dependent on COI1 (coronatine insensitive 1) mediated pathway. Eight different mutants rrb1, rrb2, rrb3, rrb4, rrb5 , rrb6, rrb7 (reduced responsiveness to avrB) and cre1 (constitutive RAP2.6 expresser) were isolated in a screen to understand the host cellular activities modulated by DC3000 type III effector avrB. The isolated mutants displayed different disease resistance profiles to Pst DC3000.; The mutant rrb4 has a mutation in OPR3 gene that codes for a 12-oxophytodienoate reductase and is required for the synthesis of JA. The avrB-induced expression of RAP2.6 gene is reduced in rrb4 mutant even though the induction of the gene with other biotic and abiotic stresses were quite normal, suggesting that the avrB specific induction of RAP2.6 gene requires JA and avrB could modulate the levels of JA during the infection process. rrb5 mutant is relatively more susceptible to Pst DC3000 and at the same time accumulates higher levels of JA. cre1 mutant which constitutively expresses the RAP2.6 transgene, codes for a putative mechanosensitive ion channel and accumulates higher levels of JA. rrb6 and rrb7 are ethylene insensitive mutants which are highly susceptible to Pst DC3000. rrb6 is found have a mutation in the EIN3 gene. The increased susceptibility of rrb6 mutant could be because of the increased stability of the EIN3 protein. Taken together, the results here support that the type III effector avrB modulates JA and ethylene-mediated pathways during the infection process. |
