The light-response BTB1 and BTB2 proteins assemble nuclear ubiquitin ligases that modify phytochrome B and D signaling in Arabidopsis.
Members of the Bric-a-Brac/Tramtrack/Broad Complex (BTB) family direct the selective ubiquitylation of proteins following their assembly into Cullin3-based ubiquitin ligases. Here, we describe a subfamily of nucleus-localized BTB proteins encoded by the LIGHT-RESPONSE BTB1 (LRB1) and LRB2 loci in Arabidopsis (Arabidopsis thaliana) that strongly influences photomorphogenesis. Whereas single lrb1 and lrb2 mutants are relatively normal phenotypically, double mutants are markedly hypersensitive to red light, but not to far-red or blue light, and are compromised in multiple photomorphogenic processes, including seed germination, cotyledon opening and expansion, chlorophyll accumulation, shade avoidance, and flowering time. This red light hypersensitivity can be overcome by eliminating phytochrome B (phyB) and phyD, indicating that LRB1/2 act downstream of these two photoreceptor isoforms. Levels of phyB/D proteins but not their messenger RNAs are abnormally high in light-grown lrb1 lrb2 plants, implying that their light-dependent turnover is substantially dampened. Whereas other red light-hypersensitive mutants accumulate phyA protein similar to or higher than the wild type in light, the lrb1 lrb2 mutants accumulate less, suggesting that LRB1/2 also positively regulate phyA levels in a phyB/D-dependent manner. Together, these data show that the BTB ubiquitin ligases assembled with LRB1/2 function redundantly as negative regulators of photomorphogenesis, possibly by influencing the turnover of phyB/D.
Department of Genetics, University of Wisconsin, Madison, Wisconsin 53706, USA.
Matthew J
MJ
Christians
Derek J
DJ
Gingerich
Zhihua
Z
Hua
Timothy D
TD
Lauer
Richard D
RD
Vierstra
D001059:Apoproteins / Q000235:genetics / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics / Q000502:physiology / Q000528:radiation effects*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D003116:Color; D018548:Cotyledon / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D004843:Epistasis, Genetic; D035264:Flowers / Q000502:physiology; D018506:Gene Expression Regulation, Plant; D056426:Genetic Loci; D018525:Germination; D008027:Light; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010834:Phytochrome / Q000235:genetics / Q000378:metabolism; D051939:Phytochrome B / Q000235:genetics / Q000378:metabolism*; D063245:Plant Development / Q000528:radiation effects; D030821:Plants, Genetically Modified / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D055550:Protein Stability; D012639:Seeds / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D015398:Signal Transduction; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination
D001059:Apoproteins; D029681:Arabidopsis Proteins; C000588971:LRB1 protein, Arabidopsis; C000588972:LRB2 protein, Arabidopsis; C000588973:LRB3 protein, Arabidopsis; D009687:Nuclear Proteins; C497952:PHYB protein, Arabidopsis; D010834:Phytochrome; D051939:Phytochrome B; C088754:PHYD protein, Arabidopsis; D044767:Ubiquitin-Protein Ligases