S-acylation of a non-secreted peptide controls plant immunity via secreted-peptide signal activation.

Small peptides modulate multiple processes in plant cells, but their regulation by post-translational modification remains unclear. ROT4 (ROTUNDIFOLIA4) belongs to a family of Arabidopsis non-secreted small peptides, but knowledge on its molecular function and how it is regulated is limited. Here, we find that ROT4 is S-acylated in plant cells. S-acylation is an important form of protein lipidation, yet so far it has not been reported to regulate small peptides in plants. We show that this modification is essential for the plasma membrane association of ROT4. Overexpression of S-acylated ROT4 results in a dramatic increase in immune gene expression. S-acylation of ROT4 enhances its interaction with BSK5 (BRASSINOSTEROID-SIGNALING KINASE 5) to block the association between BSK5 and PEPR1 (PEP RECEPTOR1), a receptor kinase for secreted plant elicitor peptides (PEPs), thereby activating immune signaling. Phenotype analysis indicates that S-acylation is necessary for ROT4 functions in pathogen resistance, PEP response, and the regulation of development. Collectively, our work reveals an important role for S-acylation in the cross-talk of non-secreted and secreted peptide signaling in plant immunity.

Protein modification: A critical modulator in the interaction between geminiviruses and host plants.

Geminiviruses are a large group of single-stranded DNA viruses that infect plants and cause severe agricultural losses worldwide. Given geminiviruses only have small genomes that encode a few proteins, viral factors have to interact with host components to establish an environment suitable for virus infection, whilst the host immunity system recognizes and targets these viral components during infection. Post-translational protein modifications, such as phosphorylation, lipidation, ubiquitination, SUMOylation, acetylation and methylation, have been reported to be critical during the interplay between host plants and geminiviruses. Here we summarize the research progress, including phosphorylation and lipidation which usually control the activity and localization of viral factors; as well as ubiquitination and histone modification which are predominantly interfered with by viral components. We also discuss the dynamic competition on protein modifications between host defence and geminivirus efficient infection, as well as potential applications of protein modifications in geminivirus resistance. The summary and perspective of this topic will improve our understanding on the mechanism of geminivirus-plant interaction and contribute to further protection of plants from virus infection.