Cell death-inducing effectors in the latent necrotrophic pathogen Cercospora zeina of maize

A total of 140 differentially expressed effector genes were identified, with most being upregulated in the mid-stage during the transition to necrotrophy. During this stage, structurally related members of the NIS1 effector family were expressed, including a previously undescribed NIS1 variant, CzNIS1b. Transient expression of CzNIS1b in Nicotiana benthamiana induced a cell death response similar to that of canonical NIS1 orthologs, despite structural models revealing an atypical α-helix at the C-terminus.</p><p><br></p><p dir="ltr">To identify additional cell death-inducing effectors, structural phylogenetics was used to define effector structural families (ESFs) and identify candidate secreted effector proteins (CSEPs) from C. zeina with potential cell death-inducing activity.

C. zeina CSEPs clustering with functionally characterized cell death-inducing effector orthologs within ESFs were hypothesized to induce cell death when transiently expressed in Nicotiana benthamiana. Indeed, C. zeina CSEPs from three distinct cell death-inducing families were chosen for biological validation and shown to induce cell death in N. benthamiana. Expression analysis showed that C. zeina ESFs generally contained no more than two highly expressed genes, suggesting limited structural redundancy and the possibility for effector gene silencing during infection. </p>