A genetic screen for mutants defective in @entity61434 -LUC degradation in XXXX reveals an important requirement for TOPOISOMERASE6B in auxin physiology.

@entity958 @entity61435 @entity50339 @entity61434
Many plant growth and developmental processes are modulated by the hormone auxin. Auxin-modulated proteolysis of Aux/IAAs, a family of transcriptional repressors, represents a major mode of auxin action. Auxin facilitates the interaction of Aux/IAAs with @entity50339 /AFB F-box proteins, promoting their ubiquitination by the SCF( @entity50339 /AFB) ubiquitin E3 ligase leading to subsequent degradation by the 26S proteasome. To identify new genes regulating Aux/IAA proteolysis in @entity958 , we took a genetic approach, identifying individuals with altered degradation of an @entity61434 -luciferase fusion protein ( @entity61434 -LUC). A mutant with 2-fold slower @entity61434 -LUC degradation rate compared with wild-type was isolated. Positional cloning identified the mutant as an allele of TOPOISOMERASE6B, named @entity61435 -7. @entity61435 encodes a subunit of a plant and archea-specific enzyme regulating endoreduplication, DNA damage repair and transcription in plants. T-DNA insertion alleles ( @entity61435 -8 and @entity61435 -9) were also analyzed. @entity61435 -7 seedlings are less sensitive to exogenous auxin than wild-type siblings in primary root growth assays, and experiments with DR5:GUS. Additionally, @entity61435 -7 seedlings have a 40% reduction in the amount of endogenous IAA. These data suggest that increased @entity61434 -LUC half-life in @entity61435 -7 probably results from a combination of both lower endogenous IAA levels and reduced sensitivity to auxin.
