Plant and Cell Physiology Advance Access originally published online on February 8, 2007
Plant and Cell Physiology 2007 48(3):498-510; doi:10.1093/pcp/pcm021
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MAP Kinases Function Downstream of HSP90 and Upstream of Mitochondria in TMV Resistance Gene N-Mediated Hypersensitive Cell Death
1National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki, 305-8602 Japan
2National Agricultural Research Center, Tsukuba Ibaraki, 305-8666 Japan
*Corresponding author: E-mail, mituhara{at}affrc.go.jp; Fax, + 81-29-8387469.
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Abstract |
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Although the involvement of heat shock protein 90 (HSP90), mitogen-activated protein kinase (MAPK) cascades and organelle dysfunction in plant hypersensitive cell death has been suggested, the mutual relationship among them has not been elucidated. Here, we show the molecular network of HSP90, the wound-induced protein kinase (WIPK)/salicylic acid-induced protein kinase (SIPK)-mediated MAPK cascade and mitochondrial dysfunction in tobacco mosaic virus (TMV) resistance gene N-dependent cell death. p50, the Avr component for N, NtMEK2DD, a constitutively active form of a MAPK kinase of WIPK/SIPK, and a mammalian pro-apoptotic factor Bax were used for cell death induction. Suppression of HSP90 and treatment with geldanamycin, a specific inhibitor of HSP90, compromised p50- but not NtMEK2DD- or Bax-mediated cell death accompanying the reduction of NtMEK2, WIPK and SIPK activation. In WIPK/SIPK-double knockdown plants, p50- and NtMEK2DD- but not Bax-mediated cell death was suppressed. All three types of cell death induced mitochondrial dysfunction, but they were similarly suppressed by Bcl-xL, which is a mammalian anti-apoptotic factor, and prevents mitochondrial dysfunction in plants as it does in animals in the cell death signal pathway. Taken together with the expression profile of hypersensitive reaction marker genes, it was indicated that the MAPK cascade functions downstream of HSP90 and transduces the cell death signal to mitochondria for N gene-dependent cell death. Furthermore, we found that WIPK and SIPK are functionally redundant in cell death signaling using WIPK/SIPK single or double knockdown plants.
Keywords: Heat shock protein 90 - Mitochondria - Mitogen-activated protein kinase - Programmed cell death - Signal transduction - Transient expression
Abbreviations: GDA, geldanamycin; HR, hypersensitive reaction; HSP, heat shock protein; MAPK, mitogen-activated protein kinase; MAPKK, MAPK kinase; MAPKKK, MAPKK kinase; MBP, myelin basic protein; PR, pathogenesis-related; Rh123, rhodamine123; RNAi, RNA interference; SIPK, salicylic acid-induced protein kinase; TMV, tobacco mosaic virus; VIGS, virus-induced gene silencing; WIPK, wound-induced protein kinase
(Received December 25, 2006; Accepted February 1, 2007)
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