Constitutive Expressor Of Pathogenesis-related Genes5 affects cell wall biogenesis and trichome development.

The Arabidopsis thaliana CONSTITUTIVE EXPRESSOR OF PATHOGENESIS-RELATED GENES5 (CPR5) gene has been previously implicated in disease resistance, cell proliferation, cell death, and sugar sensing, and encodes a putative membrane protein of unknown biochemical function. Trichome development is also affected in cpr5 plants, which have leaf trichomes that are reduced in size and branch number. In the work presented here, the role of CPR5 in trichome development was examined. Trichomes on cpr5 mutants had reduced birefringence, suggesting a difference in cell wall structure between cpr5 and wild-type trichomes. Consistent with this, leaf cell walls of cpr5 plants contained significantly less paracrystalline cellulose and had an altered wall carbohydrate composition. We also found that the effects of cpr5 on trichome size and endoreplication of trichome nuclear DNA were epistatic to the effects of mutations in triptychon (try) or overexpression of GLABRA3, indicating that these trichome developmental regulators are dependant on CPR5 function for their effects on trichome expansion and endoreplication. Our results suggest that CPR5 is unlikely to be a specific regulator of pathogen response pathways or senescence, but rather functions either in cell wall biogenesis or in multiple cell signaling or transcription response pathways.