New Phytologist (2012) 196, 4-6

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Andrea Mair and Markus Teige (2012)
Shaping the pathogen response by protein kinase triggered oxidative burst
New Phytologist 196 (1), 4-6
Abstract: Plants are able to protect themselves against pathogen attack in many different ways. One key mechanism involved is the rapid production of reactive oxygen species (ROS; Alvarez et al., 1998) and nitric oxide (NO; Delledonne et al., 1998). It has been shown that Ca²⁺ signals, as well as different protein kinase pathways, trigger the generation of ROS by phosphorylation and activation of the plasma membrane NADPH oxidase RBOH (respiratory burst oxidase homolog; Kobayashi et al., 2007; Asai et al., 2008). In this issue of the New Phytologist, Kobayashi et al. (pp. 223-237) show that the calcium-dependent protein kinase StCDPK5 triggers the production of ROS in response to pathogen infection in potato (Solanum tuberosum), which results in resistance to the near-obligate hemibiotrophic pathogen Phytophtera infestans but increases the susceptibility to the necrotrophic pathogen Alternaria solani. It has long been suggested that contrasting molecular mechanisms of defense are employed against biotrophic and necrotrophic pathogens (Glazebrook, 2005), acting mostly antagonistically (Robert-Seilaniantz et al., 2011). The rapid production of ROS, accompanied by the hypersensitive response (HR), a type of programmed cell death (PCD), and also by salicylic acid (SA)-dependent defenses, is most effective against biotrophic pathogens, whereas ethylene (ET)- and/or jasmonate (JA)-dependent processes seem to act mostly against necrotrophic pathogens. The current study of Kobayashi et al. is based on the conditional expression of a constitutive active variant of the potato calcium-dependent protein kinase (CDPK) StCDPK5, which is composed of the N-terminal variable domain and the serine/threonine protein kinase domain (VK). Owing to the lack of the regulatory C-terminal junction and calmodulin-like domain, this kinase shows constitutive activity in the absence of Ca²⁺ (Cheng et al., 2002; Harper et al., 2004). Similarly, ectopic expression of a truncated NtCDPK2VK variant in Nicotiana benthamiana has been used before to demonstrate the role of CDPKs in pathogen response (Ludwig et al., 2005) and revealed that NtCDPK2VK triggered ROS production and PCD and also JA and ET signaling, but not SA-dependent responses. In 2007, Kobayashi et al. (2007) identified that Ser-82 and Ser-97 in the N-terminus of the potato NADPH oxidase StRBOHB are phosphorylated in a Ca²⁺-dependent manner by StCDPK4 and StCDPK5 and that ectopic expression of StCDPK5VK triggered ROS production in N. benthamiana leaves, suggesting that StCDPK5 induces the phosphorylation of StRBOHB and regulates the oxidative burst. However, further analysis of this CDPK-mediated signaling pathway in planta was hampered by the fact that the expression of such constitutively active kinase variants leads to PCD.
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Research topic(s) for pests/diseases/weeds:
resistance/tolerance/defence of host

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Phytophthora infestans	Potato (Solanum tuberosum)
	Alternaria solani	Potato (Solanum tuberosum)