A Synthetic Peptide Encoded by a Random DNA Sequence Inhibits Discrete Red Light Responses

We have identified a synthetic peptide that interrupts discrete aspects of seedling development under red light. Previous reports have demonstrated that plants transformed with random DNA sequences produce synthetic peptides that affect plant biology. In this report one specific peptide is characterized that inhibits discrete aspects of red-light-mediated Arabidopsis thaliana development during photomorphogenesis. Seedlings expressing the PEP6-32 peptide presented longer hypocotyls and diminished cotyledon expansion when grown under red light. Other red-light-mediated seedling processes such as induction of Lhcb (cab) transcripts or loss of vertical growth remained unaffected. Long-term responses to red light in PEP6-32 expressing plants, such as repression of flowering time, did not show defects in red light signaling or integration. A synthesized peptide applied exogenously induced the long-hypocotyl phenotype under red light in non-transformed seedlings. The results indicate that the PEP6-32 peptide causes discrete cell expansion defects during early seedling development in red light, mimicking weak phyB alleles in some aspects of seedling photomorphogenesis. The findings demonstrate that new chemistries derived from random peptide expression can modulate specific facets of plant growth and development.One Sentence SummaryA plant line expressing random DNA sequence expresses a synthetic peptide that affects specific red-light responses in a developing seedling.