Modification of CUL3 by Related to Ubiquitin (RUB) is partially regulated by the Phytochrome B pathway in Arabidopsis thaliana.

Abstract

Plant growth and development depends on detecting the different wavelengths in the electromagnetic spectrum in order to perceive light conditions and grow accordingly. Phytochrome B, a red and far‐red light photoreceptor in plants, plays an integral role in shade avoidance, flowering time, seed germination, and de‐etiolation. Proper degradation of this photoreceptor and the immediate downstream signaling components, the Phytochrome Interacting Factors (PIFs), is crucial to the function of these processes and occurs via the ubiquitin‐proteasome system. The Light Regulating Bric‐a‐Brac/Tramtrack/Broad Complex proteins (LRB1 and LRB2) interact with CUL3 to form an E3 ligase complex which facilitates the attachment of ubiquitin to phytochrome B and PIF proteins. In plants, cullin‐based E3 ligase activity is dependent on the attachment of RUB (the plant ortholog of NEDD8 in human and other species) to cullin. We found that the LRB proteins contain two highly conserved regions near the N‐terminus which are similar to regions on CUL1/2 and RBX1, and these regions may play a role in the Rubylation process. Further investigation determined that the levels of Rub‐modified CUL3 are modulated by red light, and the PhyB signaling pathway plays a role in this process. To determine if the N‐terminal region of the LRBs play a role in rubylation of CUL3, a truncated version of the LRB gene missing this highly conserved region was inserted into wild type and a lrb1 lrb2 double mutant in Arabidopsis thaliana. Phenotypic, genetic, and immunoblot analysis of homozygous lines featuring the truncated LRBs suggest that the N‐terminal region may affect the ability of the LRBs to regulate red light responses. Future analysis of this region will provide insight into its role in phytochrome degradation and rubylation of CUL3.Support or Funding InformationThis research is funded by an S3 Summer Scholars Grant through the Office of Undergraduate Research at Grand Valley State University