Chapter 5 - The POLARIS Peptide

Abstract

This chapter discusses the role of POLARIS (PLS) peptide in plants. The POLARIS peptide was identified in the plant species Arabidopsis thaliana by promoter trapping. The N-terminal 24 amino acids of the PLS peptide are predicted to form two β-sheets, and the C-terminal 12 amino acids are predicted to form α-helical domain. The promoter trap strategy we developed involved transforming populations of plants with a promoterless gusA gene engineered into a T-DNA vector, allowing agrobacterium-mediated gene transfer. The gene encodes an mRNA of ca. 600 bases, at the 3´ end of which is a 36-amino-acid open reading frame (ORF). Translation of the ORF is required for biological activity. The transcriptional start of the gene overlaps with the 3´ UTR of an upstream gene. Expression of the POLARIS gene is strongest in root tips but is also detectable in young leaves and is induced by auxin. Mutation of POLARIS leads to several developmental defects, including a short root phenotype and reduced vascular complexity in leaves. The POLARIS peptide represents a new component required for cross-talk between more conventional plant signaling pathways, and modulation of its expression plays a significant role in the modulation of growth.