Poster: Plant Pathogen/Symbiont Interactions

Abs # 705: Nicotiana benthamiana gp91 phox homologs NbrbohA and NbrbohB participate in H₂O₂ accumulation and resistance to Phytophthora infestans

Presenter:	Yoshioka, Hirofumi , hyoshiok@agr.nagoya-u.ac.jp
Authors	Yoshioka, Hirofumi  (A)   Numata, Noriko  (A)   Ikeda, Naoki  (A)   Nakajima, Kazumi  (A)   Katou, Shinpei  (A)   Kawakita, Kazuhito  (A)   Rowland, Owen  (B)   Jones, Jonathan D. G. (B)   Doke, Noriyuki  (A)
Affiliations:	(A): Graduate School of Bioagricultural Sciences, Nagoya University (B): Sainsbury Laboratory, John Innes Centre

The rapid production of active oxygen species (AOS) is a characteristic early feature of the hypersensitive response (HR) during incompatible interactions between resistant plants and avirulent pathogens. AOS are responsible for triggering defense responses in plants. Respiratory burst oxidase homologs (rboh genes) have been implicated in AOS generation. We have isolated two rboh cDNAs, NbrbohA and NbrbohB, from Nicotiana benthamiana leaves. NbrbohA was expressed constitutively at a low level and the transcripts were elevated after mechanical stress of control leaf infiltration, whereas NbrbohB gene was specifically induced by the protein elicitor INF1 from the potato pathogen, Phytophthora infestans. We examined the function of the Nbrboh genes in AOS generation and in defense response by employing virus-induced gene silencing (VIGS). VIGS indicated that both genes are required for H₂O₂ accumulation and for resistance to P. infestans. VIGS of Nbrboh genes also led to a reduction and delay of HR cell death caused by INF1. We further demonstrate that induction of HR-like cell death by overexpression of a constitutively active mutant of a mitogen-activated protein kinase (MAPK) kinase, MEK^DD, which activates endogenous salicylic acid-induced protein kinase (SIPK) and wound-induced protein kinase (WIPK), is compromised by VIGS of NbrbohB. We found that MEK^DD induced the NbrbohB gene but not the NbrbohA gene. In addition, we confirmed that VIGS of SIPK/WIPK compromised the INF1-mediated HR cell death as well as MEK^DD-mediated HR-like cell death in N. benthamiana. This work provides the genetic evidence for the involvement of a MAPK cascade in the regulation of rboh genes.