The amino acids which make up proteins and peptides exist in either L or D chirality. The vast majority of proteins and peptides found in nature consist of L chirality amino acids. As a consequence, D-peptides are resistant to degradation in biological environments and thus attractive candidates as therapeutics in clinical applications. However, L and D peptides of the same amino acid composition often behave distinctly due to chiral differences; mimicking the biological behavior of a L-peptide with a D- peptide requires explicit design and experimentation. Outside of clinical applications, peptides also have application in plant biotechnology but thus far, D-peptides lack investigation for plant biotechnology. Here we mimic a naturally occurring L-peptide called flg22, a peptide released by pathogenic plant bacteria which serves as a potent signal of infection and temporarily activates plant immune defenses. We sought to extend the duration of plant immune activation by computationally designing a D-peptide mimic of flg22 using a previously reported design method developed for mammalian cells. We demonstrate successful mimicking of flg22 with a D-peptide by reconstituting the immune, physical, and transcriptional response of plants to native L-peptide flg22 exposure. First, we demonstrate pre-exposure to D-peptide flg22 significantly reduces subsequent infection of plants by the pathogen Pseudomonas syringae in a dose dependent manner. We further demonstrate D-peptide flg22 elicits longer term resistance to pathogen infection compared to L-peptide flg22, likely due to the persistence of D-peptides. Next, we characterize the transcriptional response of plants to D-peptide flg22 exposure with RNA sequencing, demonstrating native L-peptide flg22 and D-peptide flg22 elicit similar transcriptional responses. Finally, we explore the physiological response of plants to D-peptide flg22 exposure. We demonstrate D-peptide mimics could enable long-term pathogen resilience in plants and further provide a foundation for the development of other D-peptides for plant biotechnology applications.
