ALY proteins participate in multifaceted Nep1(Mo)-triggered responses in Nicotiana benthamiana and Arabidopsis thaliana

Previously, it was found that Nep1(Mo) (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 Nep1(Mo)-induced cell death could be inhibited by the virus-induced gene silencing of NbALY916 in N. benthamiana. NbALY916-silenced plants showed impaired Nep1(Mo)-induced stomatal closure, decreased Nep1(Mo)-induced production of hydrogen peroxide (H(2)O(2)) and nitric oxide (NO) in guard cells, and reduced Nep1(Mo)-induced resistance against Phytophthora nicotianae. It also found that the deletion of AtALY4, an orthologue of NbALY916 in Arabidopsis thaliana, impaired Nep1(Mo)-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 H(2)O(2) and sodium nitroprusside (an NO donor), and both Nep1(Mo) and H(2)O(2) stimulated guard cell NO synthesis. Conversely, NO-induced stomatal closure was found not to require H(2)O(2) synthesis; and NO treatment did not induce H(2)O(2) production in guard cells. Taken together, these results demonstrate that the NbAlY916/AtAlY4–H(2)O(2)–NO pathway mediates multiple Nep1(Mo)-triggered responses, including stomatal closure, HCD, and defence-related gene expression.