摘要
In tomato, the NBARC-LRR resistance （R） protein Prf acts in concert with the Pto or Fen kinase to determine immunity against Pseudomonas syringae pv. tomato （Pst）. Prf-mediated defense signaling is initiated by the recognition of two sequence-unrelated Pst-secreted effector proteins, AvrPto and AvrPtoB, by tomato Pto or Fen. Prf detects these inter- actions and activates signaling leading to host defense responses including localized programmed cell death （PCD） that is associated with the arrest of Pst growth. We found that Prf variants with single amino acid substitutions at D1416 in the IHD motif （isoleucine-histidine-aspartic acid） in the NBARC domain cause effector-independent PCD when transiently expressed in leaves of Nicotiana benthamiana, suggesting D1416 plays an important role in activation of Prf. The N-ter- minal region of Prf （NPrf） and the LRR domain are required for this autoactive Prf cell death signaling but dispensable for accumulation of the PrfD1416V protein. Significantly, co-expression of the Prf LRR but not NPrf, with PrfD1416v, AvrPto/Pto, AvrPtoB/Pto, an autoactive form of Pro （PtoY207D）, or Fen completely suppresses PCD. However, the Prf LRR does not in- terfere with PCD caused by Rpi-blblD475v a distinct R protein-mediated PCD signaling event, or that caused by overex- pression of MAPKKKα, a protein acting downstream of Prf. Furthermore, we found the PrfD1416V protein is unable to accumulate in plant cells when co-expressed with the Prf LRR domain, likely explaining the cell death suppression. The mechanism for the LRR-induced degradation of PrfD1416V is unknown but may involve interference in the intramo- lecular interactions of Prf or to binding of the unattached LRR to other host proteins that are needed for Prf stability.
In tomato, the NBARC-LRR resistance （R） protein Prf acts in concert with the Pto or Fen kinase to determine immunity against Pseudomonas syringae pv. tomato （Pst）. Prf-mediated defense signaling is initiated by the recognition of two sequence-unrelated Pst-secreted effector proteins, AvrPto and AvrPtoB, by tomato Pto or Fen. Prf detects these inter- actions and activates signaling leading to host defense responses including localized programmed cell death （PCD） that is associated with the arrest of Pst growth. We found that Prf variants with single amino acid substitutions at D1416 in the IHD motif （isoleucine-histidine-aspartic acid） in the NBARC domain cause effector-independent PCD when transiently expressed in leaves of Nicotiana benthamiana, suggesting D1416 plays an important role in activation of Prf. The N-ter- minal region of Prf （NPrf） and the LRR domain are required for this autoactive Prf cell death signaling but dispensable for accumulation of the PrfD1416V protein. Significantly, co-expression of the Prf LRR but not NPrf, with PrfD1416v, AvrPto/Pto, AvrPtoB/Pto, an autoactive form of Pro （PtoY207D）, or Fen completely suppresses PCD. However, the Prf LRR does not in- terfere with PCD caused by Rpi-blblD475v a distinct R protein-mediated PCD signaling event, or that caused by overex- pression of MAPKKKα, a protein acting downstream of Prf. Furthermore, we found the PrfD1416V protein is unable to accumulate in plant cells when co-expressed with the Prf LRR domain, likely explaining the cell death suppression. The mechanism for the LRR-induced degradation of PrfD1416V is unknown but may involve interference in the intramo- lecular interactions of Prf or to binding of the unattached LRR to other host proteins that are needed for Prf stability.
基金
the University of Idaho Startup funding to F.X.,the Knowledge Innovation Program of Chinese Academy of Sciences (KSCX2-EW-J-22) to X.M.,the National Science Fund for Distinguished Young Scholars (No.30825030) to Y.L.,and the National Science Foundation grant (DBI-0605059) to G.B.M
