Autophagy regulates programmed cell death during the plant innate immune response

Speaker:李秀儀                             Time: PM 2:00~3:00; 03/08/2006

Commentator:林以行 老師                    Room: 601

Abstract:

Plants are attacked by many disease-causing organisms including bacteria, fungi, viruses, and nematodes. Thus, they resist pathogen attacks by inducing defense responses. One of the inducing defense responses is the hypersensitive response (HR) cell death, which is often observed during the plant-microbe interaction. HR cell death is a form of programmed cell death (PCD) similar to apoptotic cell death in animal cells, which is trigged by resistance (R) protein that recognizes pathogen encoded avirulence (Avr) protein. In this paper, the authors chose the N signaling pathway inNicotiana benthamiana (NN) plants as their model which is induced by N protein (a resistance protein) that recognizes the 50kDa helicase domain (an Avr protein in tobacco mosaic virus). They used virus-induced gene silencing (VIGS) to identify components in N signaling pathway by forward and reverse genetic screens. In these screens, they found a similar autophagy gene, Nicotiana benthamiana BECLIN 1 (NbBECLIN1), and confirmed its function in autophagy and senescence. Then, they observed that BECLIN 1-silenced plants which were infected by GFP-tagged TMV showed overactive HR PCD response while healthy leaves undergo unrestricted PCD. This observation proved that BECLIN 1 was required for limiting TMV-induced cell death in the infection site. Finally, the authors demonstrated that the infected wild type plants showed increase of autolysosomes but BECLIN 1-silenced plants did not. This result indicated that autophagy was induced during the N-mediated defense response. In addition, the autophagy related genes, calss III phosphoinisitide 3 kinase (PI3K)/VPS34, ATG3, and ATG7 are also required for inducing restriction HR PCD response in TMV infection. In summary, autophagy plays an important role in plant innate immunity and regulates HR PCD.

References

1. Lam, E. et al. (2004). Controlled cell death, plant survival and development. Nat. Rev. Mol. Cell Biol. 5, 305-315.

2. Liu, Y. et al. (2005). Autophagy regulates programmed cell death during the plant innate immune responses. Cell 121, 567-577.