Pathogen elicitor peptide (pep), systemin, and their receptors in tomato: sequence analysis sheds light on standing disagreements about biotic stress signaling components

Peps are endogenous damage-associated polypeptides that evoke defense responses in plants. Like other damage-associated molecular patterns, Pep signals are transduced by receptors. PEPRs are the receptors that transduce Pep danger signals. This paper identifies new putative Peps in the Solanaceae (including Solanum spp., Nicotiana spp., and Petunia spp.) and Coffea and explores their properties. Using these newly identified Peps we derive sequence logos that present a refinement of the current understanding of the importance of specific residues in the Pep signaling molecules in Solanaceae, including several arginines, prolines that restrict peptide's conformations, and C-terminal asparagine. We examine the degree of disorder in Pep, which is likely important to the mechanism of Pep perception. This work also calls into question some of the evolutionary relationships between Peps in Solanaceae and specific Arabidopsis Peps published in previous literature, culminating in a conclusion that SlPep should not be named SlPep6 due to the lack of conservation of protein sequences in AtPROPEP6 and SlPROPEP, and that SlPep probably does not have two receptors in tomato, based on phylogenetic analysis. Our analyses advance understanding of the Pep signaling system in Solanaceae.