CYSTM, a Novel Non-Secreted Cysteine-Rich Peptide Family, Involved in Environmental Stresses in Arabidopsis thaliana.

The cysteine-rich transmembrane module (CYSTM) is comprised of a small molecular protein family that is found in a diversity of tail-anchored membrane proteins across eukaryotes. This protein family belongs to novel uncharacteristic non-secreted cysteine-rich peptides (NCRPs) according to their conserved domain and small molecular weight, and genome-wide analysis of this family has not yet been undertaken in plants. In this study, 13 CYSTM genes were identified and located on five chromosomes with diverse densities in Arabidopsis thaliana. The CYSTM proteins could be classified into four subgroups based on domain similarity and phylogenetic topology. Encouragingly, the CYSTM members were expressed in at least one of the tested tissues and dramatically responded to various abiotic stresses, indicating that they played vital roles in diverse developmental processes, especially in stress responses. CYSTM peptides displayed a complex subcellular localization, and most were detected at the plasma membrane and cytoplasm. Of particular interest, CYSTM members could dimerize with themselves or others through the C-terminal domain, and we built a protein-protein interaction map between CYSTM members in Arabidopsis for the first time. In addition, an analysis of CYSTM3 overexpression lines revealed negative regulation for this gene in salt stress responses. We demonstrate that the CYSTM family, as a novel and ubiquitous non-secreted cysteine-rich peptide family, plays a vital role in resistance to abiotic stress. Collectively, our comprehensive analysis of CYSTM members will facilitate future functional studies of the small peptides.