I will describe the natural, stepwise evolutionary journey that lead to the creation of a novel, functional peptide in sunflower seeds. This peptide, Sunflower Trypsin Inhibitor‑1 (SFTI‑1) originates within the same coding sequence as a seed storage albumin called PawS1 and is matured by the same processing enzyme that the albumin uses (1). This enzyme asparaginyl endopeptidase (AEP) has evolved in some species to cleave a tail peptide from precursor sequences and couple this to a transpeptidation reaction to make macrocyclic peptide products instead of linear products (2).
I used de novo transcriptomics (3) to trace the evolutionary history of PawS1 genes to gain insight into how this peptide was born within the albumin over millions of years. The progenitor of PawS1 appears to be a normal albumin. My data suggests an albumin sequence was interrupted by a genetic insertion event(s) ~45 million years ago to create an ancestral form of PawS1 we called PawS-Like (PawL1) (4). Subsequently, a series of genetic events evolved PawL1 into a sequence that could yield stable peptides and later still acquire a biological function as a trypsin inhibitor. The seed storage protein role of PawS1 appear to be minor and it contributes little to the total albumin pool in sunflower, perhaps explaining how PawS1 had the freedom to evolve buried peptides (5).
1. Mylne JS, et al. (2011) Albumins and their processing machinery are hijacked for cyclic peptides in sunflower. Nat. Chem. Biol. 7(5):257-259. 2. Bernath-Levin K, et al. (2015) Peptide Macrocyclization by a Bifunctional Endoprotease. Chemistry & Biology 22(5):571-582. 3. Jayasena AS, et al. (2014) Next generation sequencing and de novo transcriptomics to study gene evolution. Plant Methods 10(1):34. 4. Elliott AG, et al. (2014) Evolutionary origins of a bioactive peptide buried within preproalbumin. Plant Cell 26(3):981-995. 5. Jayasena AS, Franke B, Rosengren KJ, & Mylne JS (2015) A tripartite approach identifies the major sunflower seed albumins. Theoretical and Applied Genetics (accepted manuscript).
1. Mylne JS, et al. (2011) Albumins and their processing machinery are hijacked for cyclic peptides in sunflower. Nat. Chem. Biol. 7(5):257-259. 2. Bernath-Levin K, et al. (2015) Peptide Macrocyclization by a Bifunctional Endoprotease. Chemistry & Biology 22(5):571-582. 3. Jayasena AS, et al. (2014) Next generation sequencing and de novo transcriptomics to study gene evolution. Plant Methods 10(1):34. 4. Elliott AG, et al. (2014) Evolutionary origins of a bioactive peptide buried within preproalbumin. Plant Cell 26(3):981-995. 5. Jayasena AS, Franke B, Rosengren KJ, & Mylne JS (2015) A tripartite approach identifies the major sunflower seed albumins. Theoretical and Applied Genetics (accepted manuscript).