Abstract
Previously, it was found that Nep1Mo (a Nep1-like protein from Magnaporthe oryzae) could trigger a variety of plant responses, including stomatal closure, hypersensitive cell death (HCD), and defence-related gene expression, in Nicotiana benthamiana. In this study, it was found that Nep1Mo-induced cell death could be inhibited by the virus-induced gene silencing of NbALY916 in N. benthamiana. NbALY916-silenced plants showed impaired Nep1Mo-induced stomatal closure, decreased Nep1Mo-induced production of hydrogen peroxide (H2O2) and nitric oxide (NO) in guard cells, and reduced Nep1Mo-induced resistance against Phytophthora nicotianae. It also found that the deletion of AtALY4, an orthologue of NbALY916 in Arabidopsis thaliana, impaired Nep1Mo-triggered stomatal closure, HCD, and defence-related gene expression. The compromised stomatal closure observed in the NbALY916-silenced plants and AtALY4 mutants was inhibited by the application of H2O2 and sodium nitroprusside (an NO donor), and both Nep1Mo and H2O2 stimulated guard cell NO synthesis. Conversely, NO-induced stomatal closure was found not to require H2O2 synthesis; and NO treatment did not induce H2O2 production in guard cells. Taken together, these results demonstrate that the NbAlY916/AtAlY4-H2O2-NO pathway mediates multiple Nep1Mo-triggered responses, including stomatal closure, HCD, and defence-related gene expression.
Highlights
Plants have evolved multiple defence mechanisms against phytopathogens, including the hypersensitive response (HR) and stomatal closure (Dangl et al, 1996; Lam et al, 2001; Mur et al, 2008)
It was recently demonstrated that the mitogen-activated protein kinase (MAPK) cascade is involved in Nep1Mo (Nep1 from Magnaporthe oryzae)-triggered plant responses, and the MAPK signalling associated with hypersensitive cell death (HCD) exhibits shared and distinct components with that of stomatal closure (Zhang et al, 2012a)
A common positive control is silencing of the phytoene desaturase (PDS) gene, which results in photobleaching of the silenced regions and is a readily visible phenotype
Summary
Plants have evolved multiple defence mechanisms against phytopathogens, including the hypersensitive response (HR) and stomatal closure (Dangl et al, 1996; Lam et al, 2001; Mur et al, 2008). NLPs trigger cell death and immune responses in many dicotyledonous plants (Pemberton and Salmond, 2004; Gijzen and Nurnberger, 2006; Schwessinger and Zipfel, 2008). It is believed that NLPs may associate with the outer surface of the plasma membrane to trigger the HR (Qutob et al, 2006; Schouten et al, 2008), and global gene expression analyses have revealed overlap between the responses to Nep and responses to other elicitors that lead to active ethylene and oxygen production (Bae et al, 2006). It was recently demonstrated that the mitogen-activated protein kinase (MAPK) cascade is involved in Nep1Mo (Nep from Magnaporthe oryzae)-triggered plant responses, and the MAPK signalling associated with HCD exhibits shared and distinct components with that of stomatal closure (Zhang et al, 2012a). Information on the signalling network is still fragmentary, and many important players involved in Nep1-induced plant immunity remain to be discovered
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