Plant elicitor peptides (Peps) are conserved regulators of defense responses and models for the study of damage-associated molecular pattern-induced immunity. Although present as multigene families in most species, the functional relevance of these multigene families remains largely undefined. While Arabidopsis Peps appear largely redundant in function, previous work examining Pep-induced responses in maize (Zm) implied specificity of function. To better define the function of individual ZmPeps and their cognate receptors (ZmPEPRs), activities were examined by assessing changes in defense-associated phytohormones, specialized metabolites and global gene expression patterns, in combination with heterologous expression assays and analyses of CRISPR/Cas9-generated knockout plants. Beyond simply delineating individual ZmPep and ZmPEPR activities, these experiments led to a number of new insights into Pep signaling mechanisms. ZmPROPEP and other poaceous precursors were found to contain multiple active Peps, a phenomenon not previously observed for this family. In all, seven new ZmPeps were identified and the peptides were found to have specific activities defined by the relative magnitude of their response output rather than by uniqueness. A striking correlation was observed between individual ZmPep-elicited changes in levels of jasmonic acid and ethylene and the magnitude of induced defense responses, indicating that ZmPeps may collectively regulate immune output through rheostat-like tuning of phytohormone levels. Peptide structure-function studies and ligand-receptor modeling revealed structural features critical to the function of ZmPeps and led to the identification of ZmPep5a as a potential antagonist peptide able to competitively inhibit the activity of other ZmPeps, a regulatory mechanism not previously observed for this family.

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SUMMARY Crop damage by herbivorous insects remains a significant contributor to annual yield reductions. Following attack, maize (Zea mays) responds to herbivore‐associated molecular patterns (HAMPs) and damage‐associated molecular patterns (DAMPs), activating dynamic direct and indirect antiherbivore defense responses. To define underlying signaling processes, comparative analyses between plant elicitor peptide (Pep) DAMPs and fatty acid–amino acid conjugate (FAC) HAMPs were conducted. RNA sequencing analysis of early transcriptional changes following Pep and FAC treatments revealed quantitative differences in the strength of response yet a high degree of qualitative similarity, providing evidence for shared signaling pathways. In further comparisons of FAC and Pep responses across diverse maize inbred lines, we identified Mo17 as part of a small subset of lines displaying selective FAC insensitivity. Genetic mapping for FAC sensitivity using the intermated B73 × Mo17 population identified a single locus on chromosome 4 associated with FAC sensitivity. Pursuit of multiple fine‐mapping approaches further narrowed the locus to 19 candidate genes. The top candidate gene identified, termed FAC SENSITIVITY ASSOCIATED (ZmFACS), encodes a leucine‐rich repeat receptor‐like kinase (LRR‐RLK) that belongs to the same family as a rice (Oryza sativa) receptor gene previously associated with the activation of induced responses to diverse Lepidoptera. Consistent with reduced sensitivity, ZmFACS expression was significantly lower in Mo17 as compared to B73. Transient heterologous expression of ZmFACS in Nicotiana benthamiana resulted in a significantly increased FAC‐elicited response. Together, our results provide useful resources for studying early elicitor‐induced antiherbivore responses in maize and approaches to discover gene candidates underlying HAMP sensitivity in grain crops.

Terminal divisions of myogenic lineages in the Drosophila embryo generate sibling myoblasts that found larval muscles or form precursors of adult muscles. Alternative fates adopted by sibling myoblasts are associated with distinct patterns of gene expression. Genes expressed in the progenitor cell are maintained in one sibling and repressed in the other. These differences depend on an asymmetric segregation of Numb between sibling cells. In numb mutants, muscle fates associated with repression are duplicated and alternative muscles are lost. If numb is overexpressed the reverse transformation occurs. Numb acts to block Notch-mediated repression of genes expressed in muscle progenitor cells. Thus asymmetric cell divisions are essential determinants of muscle fates during myogenesis in Drosophila